Eutrachelophis, Myers & McDowell, 2014

Myers, Charles W. & McDowell, Samuel B., 2014, New Taxa And Cryptic Species Of Neotropical Snakes (Xenodontinae), With Commentary On Hemipenes As Generic And Specific Characters, Bulletin of the American Museum of Natural History 2014 (385), pp. 1-112 : 14-43

Eutrachelophis , undescribed species Figure 4

In 1993, the late Paulo E. Vanzolini sent to Myers what he recognized as a new species of snake from Cabeceira do Rio Urucu, Amazonas, Brazil. It clearly is closely related to Eutrachelophis bassleri and seemed likely to be a different species. But it could not be so identified with assurance because (1) ocellar head and neck patterns in Eutrachelophis and other genera are somewhat variable, and (2) because it is a female collected at about 5 ° S, 65 ° W —far to the east of known bassleri localities (see map 1). Ana Lucia C. Prudente fortunately has obtained additional material that she will describe separately.

Eutrachelophis steinbachi (Boulenger) , new combination Figures 5–9 , 11–12

Rhadinaea Steinbachi Boulenger, 1905: 454 (two syntypes, female and young, from ‘‘the Province

1946.1.21.62, lectotype by present designation).

Sara, Department Santa Cruz de la Sierra, collected by Hr. J. Steinbach’’).

Aporophis melanocephalus Griffin, 1916: 171–172 (holotype CM R-18, ‘‘a female, taken at Las Juntas, Bolivia, 250 M. above sea-level, by José Steinbach in December, 1913’’).

Rhadinea steinbachi Boulenger : Dunn, 1922: 220 ( Aporophis melanocephalus placed in synonymy).

Liophis steinbachi (Boulenger) : Amaral, ‘‘1929b’’ [1930]: 174. Peters and Orejas-Miranda, 1970: 179. Myers, 1974: 22 (comment on unsatisfactory generic assignment); Myers and Cadle, 1994: 2. Dixon, 1980: 15, 20 (listed as incertae sedis).

Rhadinea steinbocki (misspelling): Clark, 1945: 428 (mention of hemipenis).

LECTOTYPE: The lectotype (fig. 5) by present designation is BMNH 1946.1 .21.62, one of the two original syntypes. It is an adult female 558 mm total length (150 mm tail length), with one preventral, 140 ventrals, 67 subcaudals. The second syntype (paralectotype) is BMNH 1946.1 .21.63, a juvenile male (fig. 6).

DIAGNOSIS: Eutrachelophis steinbachi is like E. bassleri in having 15 dorsal scale rows and a usually conspicuous pair of ocellar markings 6 on the nape. It is a larger snake (to 558 mm total length) than bassleri (, 400 mm) and is readily differentiated by details of color pattern. E. steinbachi has a pair of oblique pale markings touching the upper anterior and upper posterior edges of the eye (both lacking in bassleri ), and the dark head color extends onto the neck as unbroken dorsal and lateral stripes. E. steinbachi lacks the broken, ocellarlike nuchal collar (present in bassleri ). A lateral line of pale dashes, where present, lies on scale row 6 in steinbachi , on row 4 in bassleri . E. steinbachi differs absolutely in having a divided hemipenis with spinose tips.

DISTRIBUTION: Eutrachelophis steinbachi is known only from a small section of central Bolivia near the eastern base of the Cordillera Oriental, at elevations of perhaps 250–500 m (map 1). Its habitat has not been recorded, but presumably it is a forest species.

SPECIMENS EXAMINED: All 12 specimens seen by us were obtained by the Bolivian collectors José Steinbach and his son Francisco Steinbach over a span of years (circa 1904–1928); these were sold to several museums. Museum data for these and one additional specimen (13 total) follow (see Remarks for commentary): BOLIVIA: no data, FMNH 35662 (F. Steinbach). Department Santa Cruz: no other data, UMMZ 69550 ; Buena Vista, no elevation, FMNH 35641 (F. Steinbach, April– May , 1928) ; Buena Vista, 450 m, AMNH R-125695, UMMZ 60736 (J. Steinbach, Nov. 1923 and Jan. 1924) ; Buena Vista, 500 m, UMMZ 60734–60735 (J. Steinbach, May and Sept. 1923) ; Las Yuntas [5 Las Juntas?], 50 m, CM

6 In the variational repertory of E. steinbachi , the postparietal (nape) ocelli may lack dark edges posteriorly and be confluent with (but usually paler than) the light ground color between dorsal and lateral stripes (e.g., fig. 6).

R-18 (holotype of Aporophis melanocephalus, J. Steinbach , Nov.–Dec. 1913). Province Sara , BMNH 1946.1 .21.62 ♀, 1946.1.21.638 (♀ lectotype and juvenile 8 paralectotype of Rhadinaea steinbachi, J. Steinbach , no date, received at BMNH Oct.17, 1904, fide A.F. Stimson, in litt.) ; Province Sara , Río Sirutu [5 Río Surutú?], UMMZ 63216 (J. Steinbach, Jan. 1925) .

ADDITIONAL SPECIMEN: ‘‘ Syntypus: NMW 23106 (8) Bolivia ; gekauft von ROSEN- BERG (?)’’ fide Tiedemann and Häupl (1980: 61). Only two BMNH specimens (see above) were mentioned in the original description, so this specimen certainly is not a syntype as stated ; there seems also a question as to whether it was purchased from Rosenberg. The specimen is correctly identified, however, based on scale counts and photographs kindly supplied by J.R. Dixon (see fig. 7) ; some of Dixon’s data on NMW 23106 are incorporated in the following description .

DESCRIPTION

PROPORTIONS AND SCUTELLATION: Eutrachelophis steinbachi is a slender snake that attains a maximum known length of 558 mm. Head wider than neck; eye large, its diameter greater than distance from its anterior edge

to nostril, going about 1.3–1.5 times into length of snout. Body higher than wide, with rounded ventrolateral edges; tail slenderly tapering. The only adult male having a complete tail is 454 mm in total length, with a tail/total length ratio of 0.313; the snoutvent length of this specimen is 312 mm, which is exceeded by a broken-tail male of 345 mm SVL. Two adult females are 531 and 558 mm total length, with tail/total ratios of 0.273 and 0.269, respectively.

Juveniles have relatively shorter tails: Two females are each 185 mm total length, with identical tail/total ratios of 0.254. Two males of 211 and 222 mm total length have tail ratios of 0.270 and 0.284, respectively. A larger male 251 mm SLV and 363 mm total length (tail/total 5 0.308) is still immature, as judged from soft hemipenial spines and unenlarged kidney tubules and vasa deferentia—suggesting that sexual maturity in this species is not attained before roughly 400 mm total length.

Dorsal scales smooth, in 15-15-15 rows; anal ridges lacking; apical pits absent on several specimens carefully examined. Ventral plates 134–140 (6 males 134–136, x¯ 5 134.8; 6 females 137–140, x¯ 5 137.7). Anal plate divided. Subcaudals in 66–81 pairs (4 males, 70–81, x¯ 5 76.0; 5 females 66–73, x¯ 5 68.8).

Rostral plate wider than high, visible from above. Internasal and prefrontal plates paired, each prefrontal laterally in contact with nasal, loreal, and preocular. Supraocular large, about as long as frontal and more than half as wide. Frontal pentagonal or slightly hexagonal, over 1.5 times longer than wide, equal or slightly longer than distance to snout. Interparietal suture varying from conspicuously shorter than to nearly equal length of frontal. Loreal higher than wide, tending in shape toward a slanting rhomboid. One high, narrow preocular, rarely two (on one side only in one specimen); two postoculars, the lower being smaller. Temporals 1 + 2 (one specimen with 2 + 2 + 3 on one side of head). Eight supralabials, with labial 2 touching loreal and labials 3–5 bordering eye. Infralabials variable, range 9–11, but counts differing on left and right sides in six of seven specimens; first pair in contact behind mental. Tiny inconspicuous tubercles on head plates and chin.

COLOR AND PATTERN IN PRESERVATIVE: In alcohol, Eutrachelophis steinbachi is grayish brown (gray where stratum corneum has fallen away). Top and sides of head darker brown, with the dark head coloring extending posteriorly as a middorsal and pair of lateral stripes for a distance of about a fourth to a third of the body length before fading out. There are three pairs of conspicuous, blackedged white spots atop the head and nape (figs. 5–8), as follow: (1) An elongated white spot slants anterodorsally in front of the upper edge of each eye (from top of preocular onto side of prefrontal). (2) A similarly elongated white spot slants posterodorsally behind the upper edge of each eye (from upper postocular onto parietal). The oblique postocular marking may be better defined and more vivid than its preocular counterpart. (3) The third pair of black-rimmed white markings are on the nape and may appear as rounded ocelli (fig. 8) or elongated spots (fig. 5), situated posterolaterally about one scale-length behind each parietal. The pale nape ocelli, however, are not always discrete, but are often fused posteriorly with the light dorsolateral ground color adjacent to the dorsal stripe (fig. 6); this fusion occurs in eight of 12 specimens, either on one side only (3 specimens) or on both sides (5 specimens), partly determined by the undulatory courses of the dark neck stripes. The lower parts of the supralabials and underside of the head are white.

The middorsal dark stripe undergoes one to several undulations anteriorly on the neck, where it varies in width from about four to seven scale rows and sometimes fuses briefly with the lateral stripe. As the middorsal stripe straightens out it becomes edged by a line of white dashes along the middle of the sixth scale row; posteriorly the middorsal stripe starts to fade first in the center, and in some specimens may be represented all the way to the tail by a double line of black dots (sixth scale row on each side) marking its former edges. At its start, the lateral dark stripe occupies scale row 3 and adjacent halves of rows 2 and 4, but it soon narrows to a line confined to row 3 before breaking up into a series of dark dots, which extend (inconspicuously) far posteriad in a few specimens. In some individuals the lower sides posteriorly are somewhat darker than the dorsum. The body color extends onto the edges of the ventral and subcaudal plates; ventral surface otherwise immaculate white. No information is available on coloration in life.

HEMIPENIS

The following description is entirely based on retracted hemipenes (fig. 9). The uneverted left organs of AMNH R-125695 and FMNH 35662 had been opened midventrally; they were removed and pinned flat for detailed study and illustration. Supplementary notes were provided by examination of in situ organs in UMMZ 60734 and 63216.

Major retractor muscle originating at level of subcaudal 37 for the right hemipenis of FMNH 35662, anteriorly dividing at the levels of subcaudals 20 (1 specimen), 19 (2), or 15 (1), and inserting on the ends of the hemipenial lobes at subcaudals 17 (1), 15 (2), or 14 (1). The hemipenis therefore is relatively long, spanning 14–17 subcaudals. The two lobes are narrow and long, comprising nearly twothirds the total length of the hemipenis, which bifurcates at the level of subcaudal 6 in three specimens and at subcaudal 7 in another.

The extreme base of the organ is virtually nude except for a sparse distribution of spinules; a relatively deep basal groove on the dorsal wall might persist on the everted hemipenis as a basal naked pocket (sensu Myers, 1974: 32), but this is uncertain. Two large and two medium-sized spines arise across the middle of the undivided base of the organ; these spines are nearly straight, and the tips of the two largest extend nearly to the base of the hemipenis, on either side of the sulcus (fig. 9). Above the big spines are numerous small,

There is at the base of the lobes an interlobular nude space—the STB, or ‘‘smooth terminal basin’’ (see Hemipenial Terminology for Snakes)—which is closely edged by small, short spines (fig. 9). This ‘‘basin’’ has apparent expansion folds and therefore lacks the sulcuslike smoothness seen in some other taxa (e.g., compare with the STB shown in fig. 18). The expansion folds suggest that the basin will be considerably enlarged after eversion. 7

Outside the STB, the long hemipenial lobes are completely spiny as described above. The sulcus proximally lies on the lateral wall (both on left and right organs) and divides halfway up the base, at the level of subcaudal 3. The branches of the sulcus are deeply incised and have a centrifugal orientation, lying on the ventral wall of the ventral lobe and on the dorsal wall of the dorsal lobe; each sulcus branch terminates well short of the apex.

SKULL AND DENTITION: The skull was removed from one specimen of Eutrachelophis steinbachi ( AMNH R-125695). See figure 11 and text under Global Comparisons. Eight maxillae in as many specimens bear 25–28 (x¯ 5 25.6) small, subequal teeth, followed by a diastema and two offset, ungrooved fangs (fig. 12) ; maxillary fangs about twice as large as the prediastemal teeth, with knifelike rear edges. AMNH R-125695 has 19/20 palatine teeth, followed by about 34/36 pterygoid teeth; dentary teeth 35/33.

VERTEBRAE, HEAD MUSCLES, GLANDS, AND VISCERA: See under Global Comparisons.

REMARKS

As indicated above, Eutrachelophis steinbachi (Boulenger) is known to us from a dozen specimens. Excluding one specimen of straight to slightly recurved spines, those close to the sulcus being very small. The proximal 40 % –50 % of each hemipenial lobe is profusely covered by short, thick spinules. The distal 50 % –60 % of a lobe is densely covered with straight, relatively long thin spines, and the sulcus branch ends abruptly in this region, at a length about 80 % up the lobe.

7 The AMNH specimen of Eutrachelophis steinbachi was obtained by exchange. Both hemipenes had been opened, so it was not possible to obtain a manual eversion as was done for E. bassleri . The organ depicted in figure 9 suffered the same fate as that of another important specimen (see appendix 1: Hemipenis of Lectotype), but in each case there is a contralateral organ to save the day. A check of the left in situ hemipenis of AMNH R-125695 verifies that the STB was accurately drawn in figure 9. Hussam Zaher (personal commun.) manually everted the hemipenis of a MZUSP specimen of E. steinbachi ; a description or illustration showing the STB is awaited with interest.

questionable provenance, all originated over a period of time (circa 1903–1928) from the Bolivian collectors José Steinbach and his son Francisco Steinbach. Their locality designations are of a somewhat general nature, but the several Steinbach localities for this species seem to lie at the eastern base of the Andes in the department of Santa Cruz.

Buenavista (5 Buena Vista of modern maps and gazetteers) and Provincia Sara are the only localities for Eutrachelophis steinbachi shown on map 1, although the old ‘‘Province Sara’’ [Provincia Gutiérrez]—the type locality—is a region rather than a single collecting site. 8 José Steinbach lived in Buena Vista (17 ° 279S, 63 ° 409W), the most frequently mentioned locality. His locality Río ‘‘Sirutu’’ for a UMMZ specimen may be one of several spelling variants of Río Surutú, a known Steinbach locality ( Paynter, 1992: 142–143). According to Sydney Anderson (personal commun.), ‘‘The most probable collecting areas near the Río Surutú would have been reasonably near the town of Buenavista … probably to the west or southwest of that village.’’

The locality for one specimen sent to the Carnegie Museum was given by Steinbach as Las Yuntas, 250 m., Dpto. Santa Cruz de la Sierra (fide C.J. McCoy, in litt.) ; 9 this became the type of Aporophis melanocephalus , described by Griffin (1916), who failed to publish the department and who changed ‘‘ Las Yuntas’ ’ to ‘‘Las Juntas.’’ The last is in fact the modern Bolivian name for at least one town previously with the former spelling, but there are at least two places with the name ‘‘ Las Juntas’ ’ in the western part of the department of Santa Cruz, 10 and we are

8 This subdivision of Depto. Santa Cruz has not had stable borders. The Province of Sara was larger in the early part of the 20th century than at present. It included the more recent provinces of Sara, Santiesteban, and Ichilo, which were shown on a map published in 1980 (S. Anderson, personal commun.). The name Provincia Gutiérrez appears to be a more recent replacement for Provincia Sara ( Paynter, 1992: 59, 138).

9 The Steinbachs’ ‘‘Depto. Santa Cruz de la Sierra’’ apparently is a descriptive phrase specifying the western part of the large Department of Santa Cruz —not to be confused with ‘‘ Santa Cruz de la Sierra’’ as applied to the city in the same region.

10 One Las Juntas is about 120 km SW Buena Vista, and another is about 140 km SSE Buena Vista on the Río Grande (from Mapa de la República de Bolivia, 1:1,500,000, R. Zumelzu y Cia., La Paz, 1947).

uncertain which (if either) of them is the type locality of A. melanocephalus . The holotype of melanocephalus is a juvenile female only 185 mm in total length (tail 5 47 mm) rather than ‘‘291 mm’’ (tail 47 mm) as given by Griffin; the right maxilla has been subsequently removed and shows 25 + 2 teeth; there are about 137 ventrals and 69 subcaudals.

GLOBAL COMPARISONS

Despite striking differences in their hemipenes, the very considerable external similarity between Eutrachelophis bassleri , new species, and E. steinbachi (Boulenger) is accompanied by great similarity in skull and dentition, head muscles and glands, and general visceral anatomy. The vertebrae are also similar, with a ventral keel but no hypapophysis on the posterior vertebrae; neither species shows any suggestion of winglike or shelflike expansions on the zygapophyses or any expansion of the distal edge of the moderately high neural spine. These vertebral similarities are not so impressive, however, because they are shared with the majority of colubrid snakes. 11

VISCERA

In both species the tongue is long and extends back nearly ( E. steinbachi ) or quite ( E. bassleri ) to the heart. There is no left lung in the two specimens dissected and the trachea ends opposite the apex of the heart in both specimens. 12 In each species the pulmonary (right) lung has the usual reticulation of raised alveolar rims on its lining (rather than the essentially smooth lining surface seen in a few colubrids such as Amastridium , Compsophis , and Psammodynastes ); this alveolar reticulation is continued forward on the membranous dorsal wall of the trachea to fade into pitting and then into quite smooth membrane

11 An unfortunate consequence of this is that it is unlikely that the fossil record, which is almost entirely of vertebrae for snakes, will ever give any useful information about Eutrachelophis and the many other genera whose vertebrae are too nondescript to be surely recognizable.

12 Data on viscera, head glands and muscles, skull, and vertebrae were obtained by dissection of AMNH R-55786 ( E. bassleri ) and AMNH R-125695 ( E. steinbachi ); both adult males.

anteriorly, but in neither does this forward extension of alveolar reticulation bulge out beyond the dorsal tips of the cartilaginous tracheal semirings to form a conspicuous ‘‘tracheal lung.’’ In E. bassleri the forward extension of alveolar reticulation reaches within a head length of the head, but in E. steinbachi it reaches only about a heart length anterior to the heart. Thus, both species of Eutrachelophis seem to fall in the intermediate range, between Neotropical ‘‘xenodontines’’ that unequivocally have a tracheal lung (e.g., Coniophanes , Conophis , Darlingtonia , Hydrops , Rhadinaea decorata , R. laureata , Urotheca godmani ) and those that unequivocally lack a tracheal lung (e.g., Atractus major , Ialtris , Taeniophallus brevirostris , T. occipitalis ); probably the majority of ‘‘xenodontines’’ fall into the intermediate range with Eutrachelophis . The liver is separated from the heart by a moderate interval (eight ventrals in both specimens examined), as in most ‘‘xenodontines.’’ (But in a broad range of dipsadines, including Amastridium , Arrhyton vittatum , Darlingtonia , Rhadinaea calligaster , and Urotheca godmani , for example, the liver reaches forward nearly or quite to the level of the apex of the heart. At the opposite extreme, in Pseudoeryx plicatilis [AMNH R-52229] the liver is separated from the heart by 30 ventrals.)

As in other colubrids, with the exception of a few Old World genera (e.g., Boaedon , Bothrophthalmus , Liophidium , Pareas , Pseudoxyrhopus ), the rectal caecum is absent in Eutrachelophis bassleri and E. steinbachi .

The general evidence from the viscera is consistent with a close affinity between Eutrachelophis bassleri and E. steinbachi , but cannot be considered convincing evidence for close relationship because the two species are not at all unusual in visceral features and the resemblances between them are shared with many other ‘‘xenodontines.’’ It is the head structure that shows a sufficient number of shared unusual characters to make a special common ancestry the most likely explanation for the resemblances between Eutrachelophis bassleri and E. steinbachi .

HEAD GLANDS

Both species show an unusually large temporal extension of the Harderian gland, exposed behind the orbit but posteriorly inserted deep to the muscle adductor mandibulae externus superficialis and superficial to the adductor externus profundus (sensu Zaher, 1994). An equally large (and similarly placed) temporal extension of the Harderian gland also occurs in Rhadinophanes monticola (UTA R-4176) and Contia tenuis (AMNH R- 69062). In all these snakes, the deep insertion of the gland between adductores externus superficialis and profundus seems to form a functional complex, with the two muscles acting to compress and evacuate the gland; the profundus retains its usual function as a powerful adductor of the lower jaw, but the superficialis is reduced to a thin layer of fibers across the lateral surface of the rear portion of the gland and probably functions mostly—or entirely—as a compressor of the gland. Secretions from the Harderian gland discharge into the subbrillar space to lubricate the eye; the secretions also pass through the lachrymal duct into the vomeronasal (Jacobson’s) organ, for a function still speculative (e.g., Bellairs and Boyd, 1947, 1950; Minucci et al., 1992; Rehorek et al., 2003: 358 [the last authors do not identify a method for lubricating the eyeball under the brille, and only observe that ‘‘there is no nictitating membrane in the orbit of either snake species’’]).

In neither Eutrachelophis bassleri nor E. steinbachi could a rictal gland (sensu Mc- Dowell, 1986) be found, nor could any infolding of the oral mucosa just medial to quadrato-maxillary ligament that might represent a rictal gland; the quadrato-maxillary ligament ends anteriorly on the skin of the last supralabial, and so does not reach forward to the region where a rictal gland might be expected. McDowell (1986) argued that the ‘‘rictal gland’’ is the homolog of the ‘‘anterior temporal gland’’ and of at least the sheath of the venom gland of various other snakes, and that these are, in turn, homologous to the Mundplatte, or rictal fold, of lizards. Furthermore, he stated that since the lizard rictal fold is normally a long and deep invagination of oral mucosa deep to the quadrato-maxillary ligament, the absence of the rictal gland (and even of the portion of the ligament that should accompany it) in the two species of Eutrachelophis would be less lizardlike (and presumably, more specialized) than the presence of the gland; this absence would represent an unusual, but not unique, shared specialization. The gland is a minute vestige or absent in Taeniophallus brevirostris , and it could not be found in Conophis vittatus (AMNH R-65108), Contia tenuis (AMNH R-73392), Farancia abacura (AMNH R- 110941), Helicops angulatus (AMNH R- 52746), or Thamnodynastes pallidus (AMNH R-4446). In Urotheca multilineata (AMNH R-98288), at the opposite extreme, the rictal gland has become greatly expanded as a floccular, thin-walled glandular structure covering most of the temporal region just beneath the skin; although large, it is a solid mass of glandular tissue rather than a hollow pocket (thus, it is quite different in appearance from the lizard rictal fold) and may represent a secondary enlargement of the small to very small pocket seen in most ‘‘xenodontines.’’

All three species of Eutrachelophis have a well-differentiated ‘‘supralabial gland,’’ the outline of which in some preserved specimens can easily be seen through the postorbital supralabial integument, as in figure 4 (unnamed species). The gland is similarly positioned in E. bassleri and E. steinbachi , in which it is adherent to the medial side of the supralabial integument. The serous (Duvernoy’s) portion of this gland is not (to gross examination, at least) clearly differentiated from the mucous part of the gland in either species. Enlargement of the rear maxillary teeth is not accompanied by a correspondingly conspicuous differentiation of the gland, which tapers posteriorly rather than showing enlargement behind the level of the eye. Unfortunately, the serous and mucous contributions to this gland in Eutrachelophis and many other ‘‘xenodontines’’ are not distinguishable without histological preparation ( Taub, 1966, 1967).

In both named species of Eutrachelophis the lateral nasal gland is well defined and lies in a clearly defined aditus conchae of the nasal capsule—that is, in an invagination of the lateral wall of the cartilaginous capsule that forms a vertically oriented protrusion (the concha) into the lateral wall of the nasal passage; the vertical edge of this protrusion defines a lateral diverticulum (the paracapsular recess, or sakter) of the nasal cavity, housed in the prefrontal bone, with the facial wing of the prefrontal forming a partial lateral wall for the paracapsular recess, the intraorbital wing of the prefrontal forming a posterior wall for the recess, and the roof of the lachrymal canal of the prefrontal forming the floor of the recess. Two bony processes define the rim of the aditus conchae: the conchal process of the septomaxilla rises along the anteromedial rim of the aditus; and the conchal process of the prefrontal, rising from dorsomedial rim of the anterior orifice of the lachrymal canal of the prefrontal, lies along the posterolateral rim of the aditus. The above conditions are as in the great majority of ‘‘xenodontines,’’ and Colubroidea in general. But some ‘‘xenodontines’’ have reduced the nasal conchae and its aditus, so that the bulk of the lateral nasal gland lies more superficially: in Tretanorhinus nigroluteus (AMNH R- 70222) and in Coniophanes quinquevittatus (AMNH R-74493) the concha is present, but with a reduced aditus, so that much of the gland lies in a shallow depression on the side of the nasal capsule; in Apostolepis , Carphophis , Farancia , Hydrops , and Pseudoeryx , the concha (and its aditus) is only vaguely defined and the conchal process of the prefrontal is a blunt vestige or absent.

HEAD MUSCLES

Both Eutrachelophis bassleri and E. steinbachi have unusually weak jaw adductors, with the adductor externus medialis essentially confined to the lateral surface of the braincase, leaving a broad exposure of the parietal and supraoccipital between the left and right muscles.

The adductor externus superficialis (sensu McDowell, 1986 5 adductor externus profundus of most authors) and the adductor posterior are also weak muscles, so that the bony crests of the compound mandibular bone lateral (for the adductor externus superficialis) and medial (for the adductor posterior) to the mandibular adductor fossa are both low. These two mandibular adductors arise from the quadrate to insert on the mandible and therefore have the same mechanical force whether the quadrate is in the vertical (relaxed) position or is rotated outward (as when engulfing large prey); the weakness of these muscles, and of the mandibular crests for their insertion, indicates that neither species is well adapted to engulfing relatively large prey while exerting much force.

The conversion of the levator anguli oris into a compressor of the Harderian gland is mentioned above in discussion of the gland. Another unusual feature of this muscle shared by Eutrachelophis bassleri and E. steinbachi is that only the more posterior fibers of the usual colubrid levator anguli oris are retained; only those fibers that originate on the parietal are present and no fibers originate on the postorbital, nor do any fibers extend to the oral mucosa at the corner of the mouth or curve forward beneath the corner of the mouth. Diadophis punctatus (AMNH R-121701) and Liophis melanotus (AMNH R-98179) have a similar muscle, but usually the postorbital bears part of the origin of the levator anguli oris, with some of the anteriormost fibers bent forward around the corner of the mouth or inserted on the mucosa of the corner of the mouth. In some ‘‘xenodontines,’’ such as Atractus major (AMNH R-53782), Dipsas indica (AMNH R- 53780), and Helicops angulatus (AMNH R- 52746), these anterior recurrent fibers may be set off as a distinct muscle and loss of this distinct ‘‘1a’’ muscle would give the pattern seen in the two species of Eutrachelophis ; however, there is no evidence to suggest that loss of the anterior fibers in bassleri and steinbachi was preceded by segregation of the fibers in a distinct muscle.

The pterygoideus in both species is of normal colubrid form, with both the pars major and pars minor joined anteriorly at their attachment to the anterolateral corner of the ectopterygoid (directly above the enlarged rear pair of maxillary teeth), but distinct at their posterior attachment to the mandible, the insertion of pterygoideus accessorius lying just behind the mandibular attachment of the pars minor.

In both Eutrachelophis bassleri and E. steinbachi , the retractor arcus palatini is unusually slender, its origin (from the sphenoid) being slightly narrower than the origin of the retractor vomeris (also on the sphenoid, immediately anteromedial to the origin of the retractor arcus palatini). In other colubrids examined, both New and Old World, the retractor arcus palatini is at least slightly larger (usually conspicuously larger) than the retractor vomeris. The insertion pattern of the retractor arcus palatini in both bassleri and steinbachi is the pattern that is most common among colubrids: fleshily, upon the posterior shaft of the palatine and, by tendon only, upon the choanal process of the palatine. The retractor vomeris and retractor arcus palatini have origins side by side on a nearly transverse (but arched forward anteriorly) muscular line on the sphenoid, and the protractor pterygoideus arises posterior to this muscular line; thus, the protractor pterygoideus lies behind the levator bulbi group (retractor vomeris and retractor arcus palatini), as in many ‘‘xenodontines’’ (e.g., Heterodon , Thamnodynastes ), rather than extending forward on the sphenoid between the right and left levator bulbi groups (as in Atractus , Farancia , Helicops , Tretanorhinus , and many others).

Because the origins of the retractor vomeris and retractor arcus palatini muscles are arranged transversely across the sphenoid (rather than along the sphenoid-parietal contact, as they are in Diadophis , Farancia , Oxyrhopus , and many others), with the anterior orifice of the Vidian canal between the two muscles (as in Colubroidea generally), the anterior orifice of the Vidian canal is set well in from the border of the sphenoid (rather than near or on the sphenoid-parietal suture, as it is in Diadophis , Oxyrhopus , Tantalophis , and many others). The pattern of palatal muscles, both relative to one another and to the Vidian canal system of the sphenoid, is the same in both Eutrachelophis bassleri and E. steinbachi , but far from unique to them (for example, among genera related at the subfamilial level, the same pattern is seen in Thamnodynastes , but the pattern occurs also in the Madagascan Liopholidophis and Asiatic Pseudoxenodon and many other genera that probably are not closely related to the South American Eutrachelophis ). This pattern seems to indicate only a moderate forward and backward movement of the palatine-pterygoid arch and very limited (if any) ability to rotate the palatine in the vertical plane. This is in keeping with the form of the palatine bone, with a long but slender choanal process closely applied to the vomer and a long shaft of the palatine extending posterior to the attachment of the palatine to the prefrontal. The opposite extreme would be seen in those genera with the origin of the protractor extending forward to the level of the eye and the origin of the retractor arcus palatini displaced far backward behind the level of the origin of the protractor; such a pattern allows considerably greater forward and backward movement of the palatine-pterygoid arch and is usually associated with loss of the choanal process of the palatine (as in Atractus ) or with this choanal process becoming uncoupled from the vomer (as in Tretanorhinus , where the process is behind the choanae and attached by a long tether of connective tissue to the rear of the vomer).

In both Eutrachelophis bassleri and E. steinbachi , the protractor quadrati originates on the fascia covering the anterior end of the rectus capitis ventralis and there is no direct attachment to the basioccipital. In this, they resemble many other ‘‘xenodontines,’’ such as Conophis , Crisantophis , Hydrops , Liophis melanotus , Pseudoeryx , Rhadinaea decorata , and Thamnodynastes —but differ from some others, such as Adelphicos , Atractus , Dipsas indica , Heterodon , Rhadinaea flavilata , R. taeniata , Rhadinophanes , Taeniophallus brevirostris , and Tretanorhinus , where at least the most anterior fibers of the muscle are attached to the basioccipital. This seems to be a very unstable character of little taxonomic significance.

In both Eutrachelophis the cervicomandibularis has the usual colubrid insertion on the lower end of the quadrate (as a colubrid ‘‘retractor quadrati’’); in both, the depressor mandibuli has a small but distinct occipital head, broadly separated from its fellow.

Except possibly for the narrowness of the retractor arcus palatini, none of the above features of the head musculature are unique to Eutrachelophis ; overall, the head musculature of E. bassleri and E. steinbachi is much the same as in Liophis melanotus (AMNH R- 98179) and many other ‘‘xenodontines.’’ What is most impressive, however, is the close agreement between bassleri and steinbachi in the muscular details that are known to vary even among other species that appear to be closely related. The unusual common features (15 scale rows and pale head and nuchal markings), which led to our comparing these two species in the first place, do not have any obvious functional correlation with details of the head musculature and it seems implausible that bassleri and steinbachi could bear such detailed correspondence in head musculature as a result of mere coincidence of random variations.

SKULL AND DENTITION

The same argument just presented for head muscles, that concordance in characters known to be variable among ‘‘xenodontines’’ is too great to be accounted for by coincidence, has still greater force when considering the skulls of Eutrachelophis bassleri and E. steinbachi . To summarize in advance, the single skulls compared are so similar that coincidental resemblance must be rejected as an explanation.

What is most striking is that the skulls of bassleri and steinbachi combine an unusually short tabular, such as seen in some small-eyed burrowers (e.g., Atractus and Carphophis ) with a construction of the orbit associated with large-eyed snakes (e.g., Dromicodryas , Psammodynastes , Thamnodynastes ). When the details of foramina of the sphenoid and prootic are considered, there is a virtual identity between the skulls of Eutrachelophis bassleri and E. steinbachi , even though these foramina are so labile that closely related snakes may differ or, for that matter, even the left and right sides of the same skull may differ. Indeed, except for one character of the sphenoid in the orbital region (see pp. 32, 43), the single bassleri skull examined differs no more from the one steinbachi skull than might be expected for individual (including ontogenetic) variation within a single species.

This similarity is evident in the dentition, where the two skulls are nearly identical in form. In both species, the maxilla has a long series of small, evenly spaced teeth (x¯ 5 25.6 in E. steinbachi , 27.4 in E. bassleri ), followed by a diastema that is longer than the space occupied by a tooth socket, then two conspicuously enlarged, ungrooved teeth that are about twice as long as the prediastemal teeth; in both species, one of the enlarged pair of rear maxillary teeth is offset to the general line of the tooth row (fig. 12; see also fn. 1)— as is usually the case in ‘‘xenodontines,’’ but as noted in the discussion of head glands, there is no correspondingly conspicuous differentiation of Duvernoy’s gland in either species to accompany the offset rear maxillary teeth. Eutrachelophis bassleri tends to have one or two more prediastemal maxillary teeth than the larger E. steinbachi . In both skulls, the palatine (with about 19–20 teeth) and pterygoid (about 30 teeth in bassleri , 34/ 36 in steinbachi ) tooth rows form a continuous arcade of small teeth, longest on the anterior part of the palatine (where they are about equal to the adjacent maxillary teeth) and grading imperceptibly into much smaller teeth on the rear of the pterygoid. The last pterygoid tooth is approximately level with the occipital condyle in both skulls and the first palatine tooth lies just in advance of the orifice of the organ Jacobson and well behind the anterior end of the maxilla. The dentary teeth (34/ 32 in the bassleri skull, 35/ 33 in steinbachi ) very gradually diminish posteriorly, but are small even at the anterior end of the bone (about equal to the prediastemal maxillary teeth). As usual in ‘‘xenodontines’’ ( Apostolepis , Atractus , and Carphophis are among the exceptions), the last six ( E. bassleri ) or seven ( E. steinbachi ) dentary teeth are on a free posterior dentigerous limb of the dentary, behind the intramandibular hinge. None of the teeth is hinged at the base and all are of the usual pointed and recurved form.

The bones bearing the dentition are also nearly identical in E. bassleri and E. steinbachi . The maxilla has the form that is usual in colubrids, with a triangular anterior medial process that is applied to the ventral surface of the prefrontal and also is closely attached to the lateral edge of the lateral (maxillary) process of the palatine; this process of the palatine is also applied to the ventral surface of the prefrontal, just medial to the maxilloprefrontal articulation. The maxilla has a well-developed posterior medial process with its apex, directed forwardly and medially, opposite the diastema anterior to the enlarged posterior maxillary teeth. The usual (for Colubroidea) ligament runs from the apex of this posterior medial process and the adjacent medial anterior process of the ectopterygoid to the apex of the anterior medial process of the maxilla and adjacent maxillary process of the palatine. As in most ‘‘xenodontines,’’ but unlike most proteroglyphs and a number of (mostly African) colubrids, such as Boaedon , Lycophidion , and Pseudaspis , this ligament is long and runs for most of the length of the orbit; this is not merely a consequence of a long maxilla, for although a short maxilla (e.g., Heterodon , Xenodon ) will, of course, result in a short ligament, the converse is not true: Boaedon , for example, has a long maxilla but a short ligament because the posterior medial process of the maxilla (and adjacent medial anterior process of the ectopterygoid) lies well anterior to the rear of the maxilla, and the maxillary process of the palatine, which receives the anterior end of the ligament, lies well posterior to the prefrontal and to the tip of the anterior medial process of the maxilla (see appendix 2: fig. 39). In a number of snakes with a relatively short maxilla, such as Carphophis , the posterior medial process of the maxilla is extended backward, behind the tooth row, with its apex at the rear of the level of the orbit, so that the ligament (only feebly defined) is of moderate length.

The palatine is also very similar in Eutrachelophis bassleri and E. steinbachi . There is a long, narrow, transverse choanal process lying at nearly the exact middle of the palatine. This choanal process is positioned distinctly behind the level of the maxillary process and the ventral end of the prefrontal. The choanal process is entirely medial to the ventral end of the prefrontal, as usual in colubroids, in which no medial process of the prefrontal extends close to the frontal-septomaxillary joint dorsal to the palatine choanal process (unlike Dipsas indica [AMNH R-53780], Homalopsis , etc.) or functionally replaces the choanal process (as in Atractus ).

The maxillary process has a similar triangular form in both Eutrachelophis bassleri and E. steinbachi , with a sphenopalatine canal for the nerve formed by fusion of the Vidian nerve with the infraorbital branch of the maxillary (V 2) nerve, as in many, probably most, ‘‘xenodontines.’’ The posterior shaft of the palatine (that is, the portion projecting behind the choanal process to meet the pterygoid) is unusually (but not uniquely) long and slender in both species and articulates with the pterygoid at the same transverse level as the ectopterygoid-maxillary articulation, rather than well anterior to the ectopterygoid-maxillary articulation (as in, for example: Amastridium veliferum, AMNH R-114309; Hydrops marti, AMNH R-52031; Manolepis putnami, AMNH R- 58355; Oxyrhopus petola, AMNH R-52640; Rhadinaea decorata, AMNH R-107588; Taeniophallus brevirostris, AMNH R-15207) or well posterior to the ectopterygoid-maxillary articulation (as in, for example: Apostolepis flavotorquata, AMNH R-93559; Carphophis amoenus, AMNH R-75711). The articulation between the palatine and pterygoid involves a simple anterior end of the pterygoid (as usual in ‘‘xenodontines’’) that is clasped by a short ventral lip of the palatine, bearing the last palatine tooth, and a longer dorsal finger of the palatine that extends back along the dorsal surface of the pterygoid; this is the most common palatine-pterygoid articulation among ‘‘xenodontines’’ (and colubrids in general), but other forms exist, such as simple end-to-end abutment (e.g., Heterodon , Apostolepis ), or having the posterior finger of the palatine run along the medial, rather than dorsal, surface of the pterygoid (e.g., Farancia ), or subequal posterior prongs of the palatine that fit, respectively, against the medial and the lateral surfaces of the pterygoid (e.g., Hydrops ). The form of the palatine in both Eutrachelophis bassleri and E. steinbachi is very similar to that of Rhadinaea decorata (AMNH R-107588), R. fulvivittis (AMNH R-100890), and R. taeniata (AMNH R-106933), but quite different from that of Taeniophallus brevirostris (AMNH R-15207), where the choanal process has a broad base extending back almost to the level of the prongs for the pterygoid, or Urotheca multilineata (AMNH R-98288), where the slender choanal process has a distinct forward hooking of its apex and the shaft behind it is short.

Eutrachelophis bassleri and E. steinbachi have very similar pterygoid bones, as shown in the figures, but this is of less weight than the similarities in the palatine bone because differences in pterygoid bone shape are minor and subtle in ‘‘xenodontines’’ generally. The similarity in shape of the ectopteryoid between E. bassleri and E. steinbachi is more impressive, because this bone shows a wide range of form within the Xenodontinae . In both, the bone is moderately long (but conspicuously shorter than the maxilla), with a curved and cylindroid shaft that is free of the pterygoid for more than half its length and is not expanded in its posterior portion that is applied against the dorsal surface of the pterygoid. In both, the anterior end is abruptly expanded and flattened and is very asymmetrically divided, by a broadly round- ed anterior emargination, into an acutely triangular medial anterior process and a nearly rectangular lateral anterior process; the medial anterior process extends conspicuously anterior to the lateral anterior process. Thus, the two species differ from, for example, Carphophis , Contia , and Farancia , in which the medial anterior process is greatly reduced; they also differ from such ‘‘xenodontines’’ as Conophis vittatus (AMNH R- 65108) and Manolepis putnami (AMNH R-58355), in which the medial anterior process is broader—and longer—than the lateral anterior process. Downs (1967) has documented the considerable range in ectopterygoid form within the genus Geophis , where the form of the bone is distinctive of species groups within the genus. This seems to be true also of Atractus : some species (e.g., A. elaps, AMNH R-28843) have lost the lateral anterior process of the ectopterygoid but retain a long free shaft of the bone; others (e.g., A. major, AMNH R-53782) retain anterior furcation of the bone but have so shortened the free shaft that the maxilla is probably immovable relative to the pterygoid; and still others (e.g., A. trilineatus, AMNH R-101336) retain a long free shaft and also anterior furcation of the ectopter- ygoid. This variation within a single genus suggests that the form of the ectopterygoid is easily modified and that differences between two species might be expected even if the species are closely related; however, in the case of E. bassleri and E. steinbachi it is the great similarity between the two species that must be accounted for, and close phyletic relationship seems the simplest explanation.

The great similarity in the compound bone of the mandible has been noted in the discussion of the head muscles. It may be added that both species agree in having a long (for Colubroidea) retroarticular process and in the details of the splenial-angulardentary complex. In both, the Meckelian canal is open anterior to the splenial nearly to the anterior end of the dentary, as in, for example, Amastridium , Rhadinophanes , and Coniophanes fissidens (AMNH R-69977). However, in such ‘‘xenodontines’’ as Coniophanes quinquevittatus (AMNH R-74493), Rhadinaea laureata (AMNH R- 68380), and Tantalophis , the lips of the dentary forming the dorsal and ventral edges of the Meckelian exposure meet, but leave a suture, and in Liophis melanotus (AMNH R-98179), Farancia abacura (AMNH R-110941), and Apostolepis flavotorquata (AMNH R-93559) this suture fuses, at least anteriorly.

The splenial and angular are equal and moderately long; each of the bones contains a mylohyoid foramen; the splenial extends about halfway forward from the splenialangular hinge articulation to the anterior end of the dentary and the dorsal edge of the splenial is separated by a fissure from the dentary (and so, the Meckelian canal is narrowly open, even opposite the splenial). This is as in many other ‘‘xenodontines,’’ but in some others (e.g., Hydrops marti, AMNH R-52031; Oxyrhopus petola, AMNH R- 52640) the splenial is smaller, relative to the dentary, and falls well short of the halfway point between the splenial-angular hinge and the tip of the dentary; in Apostolepis , Hydrops , and Thamnodynastes , the splenial is distinctly shorter than the angular; variations in the opposite direction are seen in Coniophanes imperialis (AMNH R-77064), whose splenial is conspicuously longer than the angular, and in Farancia the splenial is unusually large relative to the dentary (but subequal in length to the angular) and extends well anterior to the midpoint between the splenial-angular hinge and the tip of the dentary. In both Eutrachelophis bassleri and E. steinbachi , the splenial has a narrow, fingerlike process that extends upward along the anterior edge of the angular; excluding that bone from the rim of the Meckelian exposure; this posterior dorsal process of the splenial is present and sharply defined in many other ‘‘xenodontines’’ (e.g., Carphophis amoenus, AMNH R-121650; Farancia abacura, AMNH R-110941; Oxyrhopus petola, AMNH R-52640; Rhadinaea decorata, AMNH R-107588; Urotheca multilineata, AMNH R-98288), but the process is absent in many others (e.g., Amastridium veliferum, AMNH R-114309; Coniophanes imperialis, AMNH R-77064; Conophis vittatus, AMNH R-65108; Hydrops marti, AMNH R-52031; Pseudoeryx plicatilis, AMNH R-52229; Thamnodynastes pallidus, AMNH R-4446). It should be noted that this tiny sliver of the splenial bone is probably of more functional importance to the feeding mechanism than its size would suggest; the posterior dorsal process of the splenial lies immediately dorsal to the condyle-cotyle articulation between the splenial and angular, a circular universal joint, the edge-to-edge contact of the posterior dorsal process of the splenial with the anterior border of the angular limits the plane of rotation of the hinge. In most ‘‘xenodontines’’ that have this process of the splenial, including Eutrachelophis bassleri and E. steinbachi , this edgeto-edge contact is diagonal to the long axis of the jaw, and so imparts a rotation of the dentary around the long axis when the intramandibular hinge is flexed (in Farancia , where the edge-to-edge contact is vertical, no such rotation around the long axis is permitted).

The construction of the orbit in both Eutrachelophis bassleri and E. steinbachi shows a pattern that has developed independently among natricines (e.g., Psammodynastes , Rhabdophis miniatus ), pseudoxyrhophiines (e.g., Dromicodryas , Thamnosophis lateralis but not Liopholidophis sexlineatus ), and other colubrids in association with a large eye and small olfactory forebrain. It may be considered a consequence of secondary enlargement of the eye, but it is not a necessary or automatic consequence, since such notably large-eyed snakes as Boiga do not show this pattern; that Leioheterodon , a relatively small-eyed Madagascar snake, shows many features of the pattern can perhaps be explained as the result of derivation from a large-eyed ancestor similar to Dromicodryas and Thamnosophis lateralis . The conspicuous features of the pattern are: 13

1. Broad entry of the parietal into the orbital rim, separating the frontal and postorbital bones but not restricting entry of the frontal into the orbital rim;

2. Elevation of the forebrain chamber, formed by the descending laminae of the frontals, well above the trabeculae (and so, there are no supratrabecular crests of the frontals or frontal contributions to the trabecular grooves);

3. The paired trabeculae lie close togeth- er, with the lamina of the [para]sphenoid that separates them thin and compressed (often, as in E. bassleri and E. steinbachi , with a defect in ossification of this thin bone, so that there is an oval fenestra in the trabecular groove of the sphenoid), and the [para]- sphenoid rostrum is narrow at mid-orbit (as seen in a ventral view of the skull), but with conspicuous suborbital flanges that extend lateral to the trabeculae and lie beneath the more posterior part of the eyeball and dorsolateral to the retractor vomeris muscles [the suborbital flange of the sphenoid provides cranial attachment for the rectus groups of eye muscles and is continued anteriorly and laterally beneath the eye by the tough but flexible orbital obturator membrane that is probably of greatest functional importance in protecting the eye from the contents of the mouth];

4. Usually (as in E. bassleri and E. steinbachi ), but not always (e.g., Conophis vittatus ), there is deficient ossification in the region of the usual frontalparietal contact in the medial wall of the orbit, dorsal to the orbital foramen

13 Since this was written, features of some of the numbered points can be seen as corroborated in Cadle (1996a: 443, figs. 38–40). –C.W.M.

(this fenestration, closed by tough connective tissue in life, makes the forebrain chamber of the frontals continuous with the orbital cavity in the dried skull);

5. Often (e.g., Dromicodryas , Psammodynastes , Thamnodynastes pallidus ) the space between the elevated forebrain chamber of the frontals and trabeculae (in grooves on the lateral surface of the [para]sphenoid rostrum) is filled in by a median crest of the [para]sphenoid, forming a functional ‘‘orbital septum’’ (but not homologous to the orbital septum of lizards, which is formed from the orbital cartilages, absent in snakes except for the portions used in construction of the cartilaginous olfactory capsules).

Of the features of the pattern just listed, Eutrachelophis bassleri does not show number 5 above; the [para]sphenoid rostrum is flat dorsally. In E. steinbachi there is a distinct crest on the dorsal side of the [para]sphenoid rostrum, but the crest is less developed than in Conophis , Crisantophis , Manolepis , and Thamnodynastes , and meets the frontals only anteriorly, leaving a triangular open chink between the [para]sphenoid crest and the frontals more posteriorly. Except for the better development of the keel on the sphenoid and the absence of a fenestra in the trabecular groove of the sphenoid, Thamnodynastes pallidus (AMNH R-4446) closely resembles E. bassleri and E. steinbachi in the construction of the orbit, but Conophis and Manolepis (these points are uncertain for Crisantophis , observed by dissection only, on AMNH R-112402) lack fenestration between the frontal and parietal, have only feeble suborbital laminae of the [para]sphenoid, and have a narrower entry of the parietal into the orbital rim, but they do have a perforation in the trabecular groove. Liophis melanotus (AMNH R-98179) approaches the pattern of E. bassleri and E. steinbachi in a different way: there is a similar fenestration between frontal and parietal, similar development of the [para]sphenoid suborbital laminae, and a similarly broad entry of the parietal into the orbital rim, but the forebrain cavity of the frontals is only slightly raised above the trabeculae posteriorly (nevertheless, the sphenoid has a low but quite distinct dorsal crest to meet the frontals here, and there is no open chink between frontals and sphenoid such as is seen in E. steinbachi ); anteriorly, the frontals rest upon the trabeculae and form weak supratrabecular ridges. A third, slighter approach to the orbital pattern of E. bassleri and E. steinbachi is made by Taeniophallus brevirostris (AMNH R-15207): the forebrain chamber is only slightly elevated above the trabeculae, but, nevertheless, the frontals are narrowly—but completely—excluded from the trabecular grooves by a narrow dorsal lip of the trabecular groove of [para]sphenoid; the parietal rather broadly excludes the frontal from the postorbital, but otherwise the orbit is quite different from that of E. bassleri and E. steinbachi , without frontal-parietal fenestration and with only feeble suborbital flanges of the [para]sphenoid.

Most Rhadinaea , sensu lato, such as R. decorata (AMNH R-107588), R. flavilata (AMNH R-50491), R. laureata (AMNH R- 68380), R. taeniata (AMNH R-106933), and Urotheca multilineata (AMNH R-98288), have frontals that rest upon the trabecular cartilages and form strong supratrabecular crests that even descend, lateral to the trabecula, to meet the ventral lip of the [para]sphenoid groove for trabecula at the front of the orbit. Many other ‘‘xenodontines’’ (and other colubroids) show this pattern, such as Amastridium , Coniophanes fissidens (AMNH R- 69977), C. imperialis (AMNH R-77064), Rhadinophanes , and Tantalophis ; or the contact of the frontal with the [para]sphenoid lateral to the trabecular cartilage may be much longer and extend for most or all of the length of the frontal supratrabecular crest as in Coniophanes quinquevittatus (AMNH R- 74493, by dissection), Adelphicos , Atractus , and Tretanorhinus . Such long contact of the frontal with the trabecula can lead to contact of the supratrabecular crest of the frontal with ventral end of the parietal beneath the orbital foramen, excluding the sphenoid from that foramen, as in Nothopsis and Hydrops . This is the usual condition in noncolubroid snakes and in many proteroglyphs and seems to be associated with a relatively small eye, at least relative to the size of the forebrain and snout. In all forms showing this ‘‘small-eyed pattern’’ the suborbital lamina of the [para]sphenoid is absent and there is no fenestration between the frontal and parietal in the medial wall of the orbit. The same may be said for those ‘‘xenodontines’’ with the ‘‘moderateeyed pattern.’’ such as Coniophanes and Rhadinaea , except that a slight suborbital flange of the [para]sphenoid may be present.

There seems, then, to be a series from the ‘‘small-eyed pattern.’’ as seen in such ‘‘xenodontines’’ as Hydrops , to the ‘‘largeeyed pattern’’ as seen in such ‘‘xenodontines’’ as Thamnodynastes . The series will not describe all the intermediates precisely, since there can be extensive fenestration of the wall of the orbit combined with the forebrain cavity resting on the trabeculae (as in Liophis melanotus ) or lack of this fenestration in combination with high elevation of the forebrain cavity above the trabeculae (as in Manolepis putnami ). Heterodon is hard to place, since it has enormous suborbital flanges of the [para]sphenoid and there is fenestration of the cranial-orbital wall (but mainly by retraction of the anterior edge of the parietal); however, the forebrain cavity seems to have been secondarily depressed toward the trabeculae (but does not touch them), so that the crest on the [para]sphenoid is concealed from external view by the frontals. Because of its long snout, Heterodon has only a ‘‘moderately’’ large eye relative to total head length, but the orbit is large relative to the unusually short braincase. In spite of these complications in surveying all ‘‘xenodontines,’’ the central point of these comparisons remains: Eutrachelophis bassleri and E. steinbachi are extremely similar to each other in orbit construction, and however the series from ‘‘small-eyed pattern’’ to ‘‘large-eyed pattern’’ is arranged, the two species under special consideration are at nearly the same step in the series, near the ‘‘large-eyed pattern’’ extreme; this in spite of the fact that neither species has exceptionally large eyes. However, the only significant skull difference between the two species occurs in the orbital region— Eutrachelophis steinbachi has a dorsal crest of the parasphenoid rostrum that is exposed below the frontals and E. bassleri does not.

Entry of the parietal into the orbital border occurs in Amastridium , Taeniophallus brevirostris (AMNH R-15207), and some Rhadinaea ( R. decorata, AMNH R-107588; R. taeniata, AMNH R-106933), but most Rhadinaea , like Adelphicos , Atractus , Coniophanes , Tantalophis , Rhadinophanes , and Tretanorhinus , have a postorbital-frontal contact excluding the parietal from the rim of the orbit. In Apostolepis (notably smalleyed snakes), the parietal enters the orbit extensively, nearly ( A. flavotorquata, AMNH R-93559) or very much ( A. erythronotus, AMNH R-62192) excluding the frontal. Parietal entry into the orbital rim is thus not a simple function of orbit size. This increases the significance of parietal entry into the orbital rim in both Eutrachelophis bassleri and E. steinbachi as a special resemblance between the two species and not a mere duplication of another character.

Eutrachelophis bassleri and E. steinbachi have very similar prefrontal bones that are unusually short anteroposteriorly, so that the vertical (frontal-to-maxillary) height is more than twice the anteroposterior dimension; this anteroposterior shortness largely reflects the weak development of the facial wing of the bone that extends forward over the lateral surface of the paracapsular (sakter) region of the cartilaginous nasal capsule. The facial wing of both E. bassleri and E. steinbachi lacks the forward extension and dorsad hooking (apomorphies of Pseudoboini ) seen in Drepanoides anomalus, AMNH R-53419, and Oxyrhopus petola, AMNH R-52640; moreover, it does not cover the preorbital area as in Hypsirhynchus ferox, AMNH R- 40124, and Manolepis putnami, AMNH R- 58355. However, the facial wing is small and obtusely pointed, with the result that the prefrontal does not have the simple and broadly convex anterior border seen in Helicops angulatus, AMNH R-56031, or the straight and vertical anterior border seen in Farancia abacura, AMNH R-110941. The attachment of the prefrontal to the frontal is as in most other ‘‘xenodontines’’ (and the great majority of colubrids): dorsally and superficially, there is a tongue-in-groove articulation, with the edge of the prefrontal fitting into a groove on the frontal; deep and ventral to this, there is a squamous overlap, with the intraorbital wing of the prefrontal fitting just behind a transversely oriented lateral eversion of the part of frontal that forms the lateral rim of the olfactory foramen (this lateral eversion of the frontal lies against the rear wall of the olfactory capsule, thus partially separating the intraorbital wing of the prefrontal from the capsule, and prevents forward rotation of the prefrontal). In both Eutrachelophis bassleri and E. steinbachi , the superficial tongue-in-groove articulation is about 30 ° from transverse in its orientation relative to the axis of the skull, with the prefrontal extended along the anterior bor- der of the frontal (but falling far short of the midline or of the nasal and permitting broad entry of the frontal into the rim of the dorsal exposure of the nasal capsule); there is no suggestion of posterior extension of the prefrontal along the lateral (orbital) border of the frontal. This is as in some other ‘‘xenodontines’’ such as Liophis melanotus (AMNH R-98179), Coniophanes fissidens (AMNH R-69977), and C. imperialis (AMNH R-77064), but the majority have the tongue-in-groove articulation oriented at 45 ° and in several (e.g., Carphophis amoenus, AMNH R-121650; Conophis vittatus, AMNH R-65108; Manolepis putnami, AMNH R-58355; Pseudoeryx plicatilis, AMNH R-52229) it is nearly longitudinal (but without backward extension of the prefrontal over the eye). In Hydrops marti (AMNH R-52031), the tongue-in-groove articulation is perfectly longitudinal and the deeper squamous articulation is absent (the lateral eversion of the frontal is missing), so that some transverse rotation of the prefrontal probably is permitted.

In both Eutrachelophis bassleri and E. steinbachi , the facet of the parietal bone bearing the postorbital bone is moderately long and oriented diagonally, approaching a vertical orientation. This is as in most ‘‘xenodontines’’ (e.g., Alsophis , Liophis , Manolepis , Rhadinaea decorata , Taeniophallus brevirostris , Urotheca multilineata , and Thamnodynastes ) and imparts an anteroposterior motion to the tip of the postorbital when that bone rotates; since the tip of the postorbital is bound by ligament to a low but distinct elevation on the dorsal edge of the maxilla (just in front of the maxillary diastema in E. bassleri and E. steinbachi and most of the others), the angle of attachment of the postorbital to the parietal probably has an indirect control over the movements of the rear of the maxilla. In some ‘‘xenodontines’’ (e.g., Atractus ) the attachment of the postorbital to the parietal is so short that it is a virtual pivot joint, and in others (e.g., Apostolepis and, according to Downs, 1967, some Geophis ) the postorbital is absent, so that the maxillary is tethered to the braincase only by a long and quite flexible ligament; this seems to be associated with a short maxilla, but is not an ‘‘automatic’’ consequence of a short maxilla, since Heterodon and Xenodon (see Kardong, 1979), both with an unusually short maxilla (but a maxilla that rotates strongly in a vertical plane), have a more or less vertical hinge attachment of the postorbital to the parietal. In some ‘‘xenodontines’’ (e.g., Adelphicos , Carphophis , Contia , Diadophis , Farancia , Hydrops , Pseudoeryx ) there is a long postorbital-parietal hinge, but oriented nearly or quite horizontally, so that rotation of the postorbital is transverse; probably this acts, through the maxillary-postorbital ligamentous connection, primarily as a check preventing excess lateral displacement of the rear of the maxilla. Still others (e.g., Amastridium , Coniophanes , Oxyrhopus , Rhadinaea flavilata ) are intermediate, with the attachment of the postorbital closer to the horizontal than in Eutrachelophis bassleri and E. steinbachi , but nonetheless distinctly inclined.

In both Eutrachelophis bassleri and E. steinbachi , the rostral complex of bones (premaxilla, nasals, septomaxillae, and vomers) is very similar and the rostral complex in both is small relative to the skull. The premaxilla has quite distinct lateral processes, but the bone is rather small (about as in Liophis melanotus, AMNH R-98179). As in Amastridium , Farancia , Hydrops , Liophis , Pseudoeryx , Rhadinaea decorata , Urotheca multilineata , and others, the premaxilla and vomer make an overlapping contact, so that the vomer participates in the support of the premaxilla (but, as is true of Colubroidea in general, is less important than the septomaxilla in this support); in many other ‘‘xenodontines’’ (e.g., Adelphicos , Apostolepis , Atractus , Carphophis , Conophis , Heterodon , Manolepis , Oxyrhopus , Rhadinaea flavilata , R. laureata , R. taeniata ), the vomer makes only a point-topoint contact with the premaxilla or is separated from that bone. In both Eutrachelophis bassleri and E. steinbachi , there is a large intervestibular fenestra, between the narial vestibules of the opposite sides and bounded anteriorly by the ascending process of the premaxilla, ventrally by the septomaxillae, and posterodorsally by the nasals; a similar intervestibular fenestra is seen in many other ‘‘xenodontines’’ (e.g., Adelphicos veraepacis , Liophis melanotus , Rhadinaea taeniata , Thamnodynastes pallidus ), but in many others (e.g., Amastridium , Apostolepis , Carphophis , Farancia , Hydrops , Rhadinaea decorata , R. laureata , Urotheca multilineata ) the intervestibular fenestra is small or absent.

Both Eutrachelophis bassleri and E. steinbachi have the usual form of hinge between the rostral complex and the frontals for ‘‘xenodontines’’: Along the cartilaginous nasal septum the septomaxilla sends back a posterior process, whose posterior tip bends strongly outward behind the passage for the vomeronasal portion of the olfactory nerve. The lateral flexure of the posterior process of the septomaxilla forms a posteriorly convex facet for the corresponding septomaxillary facet of the frontal that, in turn, is well defined by a distinct peduncle facing forward and slightly but distinctly mediad; the nasals touch the interolfactory pillar of the frontals, but without forming any articular surface, between the frontal-septomaxillary articulations and do not make any contact with the septomaxillary facets. Although most ‘‘xenodontines’’ (and other colubrids) have a similar hinge between the rostral complex and the frontals, there are some exceptions. Thus, in Apostolepis , the posterior process of the septomaxilla is stout and abuts end to end with the frontal facet; in Carphophis , the nasals are expanded and fused at their contact with the interolfactory pillar of the frontals, forming an articulation addition to the septomaxillary-frontal articulation; in Pseudoeryx and Hydrops , the nasals do not reach the frontals, nor is there any nasalfrontal contact in Atractus crassicaudatus (AMNH R-24235) or Adelphicos veraepacis (AMNH R-66961).

In both Eutrachelophis bassleri and E. steinbachi , the tip of the [para]sphenoid, just ventral to the fusion of the paired trabeculae that forms a trabecula communis, is distinctly expanded laterally and shallowly trilobated by a pair of obtuse notches. This is true also of Coniophanes , Farancia , Rhadinaea flavilata , R. laureata , R. taeniata , and many other ‘‘xenodontines.’’ It is seen also, so far as the tip of the parasphenoid is concerned, in Atractus , but in that genus the entire anterior end of the parasphenoid is broad, as in Adelphicos , Ninia , Tretanorhinus , and others, and so the tip of the parasphenoid does not appear broad relative to the interorbital portion. In others, such as Rhadinophanes and Tantalophis , as well as Adelphicos , Ninia , etc., the apex of the parasphenoid is convexly rounded anteriorly; in Amastridium and Thamnodynastes pallidus , and others, the tip of the parasphenoid is simply forked by a shallow median emargination; in Apostolepis , Carphophis , Conophis vittatus , Contia , Diadophis , Heterodon , Manolepis , and Nothopsis , the parasphenoid is pointed anteriorly.

The suborbital flanges of the parasphenoid have been noted in the preceding comparisons of the orbit; as is probably true of all snakes with a parasphenoid that is broadened to form suborbital flanges, the parasphenoid of both Eutrachelophis bassleri and E. steinbachi rises to meet the parietal lateral to the trabecular cartilages, so that the ossified bases of the trabeculae (radices trabeculae) are concealed intracranially; this is the usual condition in ‘‘xenodontines’’ (even in genera such as Atractus , Hydrops , and Pseudoeryx , with little or no development of suborbital flanges), but in some (e.g., Apostolepis , Carphophis , Farancia ), the parasphenoid appears to be narrower in this region, failing to surround the radices trabeculae laterally, and so the radices trabecular are exposed externally, lateral to the contact of the sphenoid with the more anterior part of the parietal.

The parasphenoid of both Eutrachelophis bassleri and E. steinbachi seems somewhat shorter posteriorly than in the majority of ‘‘xenodontines,’’ since it leaves the foramen for entry of the carotid artery into the pituitary fossa separate from the more lateral foramen for entry of the palatine ramus of the facial nerve into the rear of the Vidian canal. This is seen also in Liophis melanotus (AMNH R-98179) and Urotheca multilineata (AMNH R-98288), as well as in many non- ‘‘xenodontines,’’ but usually the parasphenoid of ‘‘xenodontines’’ extends back beneath these two foramina to define a common palatine nerve–carotid artery canal that forks within the sphenoid into a carotid and a Vidian canal. (In Heterodon , there is an anomalous condition, in which the posterior end of the Vidian canal is in the prootic and the single foramen in the rear of sphenoid is for the carotid artery alone. Atractus and Apostolepis also appear to have the posterior orifice of the Vidian canal within the chamber of the prootic for the trigeminal ganglion, so that only the carotid enters the large foramen in the posterior part of the sphenoid; in these forms it is probably impossible to guess the precise limits of the parasphenoid relative to the perichondral sphenoid posteriorly.) The relationships of the Vidian canal system of the sphenoid to the protractor pterygoideus and levator bulbi group of muscles have been discussed in connection with those muscles, but it may be added here that the bony canal for the palatine nerve is unusually short, as compared with other ‘‘xenodontines,’’ in both Eutrachelophis bassleri and E. steinbachi .

In both species, there is a rather large foramen (pv) in the lateral edge of the sphenoid, immediately adjacent to the sphenoid-parietal suture and well anterior to the sphenoid-prootic contact (boldface abbreviations indicate foramina shown in figs.10–11). This foramen, presumably for the pituitary vein and for the entry of the retractor pterygoideus ramus of the trigeminal nerve (V 4 levator bulbi) into the cranium is larger than that of any Rhadinaea examined, or that of Amastridium , Coniophanes , Liophis melanotus , Rhadinophanes , and Tantalophis , but similarly placed; Farancia and Thamnodynastes show close agreement with Eutrachelophis bassleri and E. steinbachi both in size and position of the foramen; in Pseudoeryx the foramen is large but more posteriorly placed, just anterior to the sphenoid-prootic contact, and in Oxyrhopus petola (AMNH R- 52640) and Hydrops marti (AMNH R-52031) the foramen lies in the parietal-prootic suture. In both Eutrachelophis bassleri and E. steinbachi , the foramen on the left side appears to be as large as that on the right side, probably indicating that the drainage from the pituitary and middle cerebral veins through this foramen is approximately equal on the left and right sides, but in Carphophis amoenus (AMNH R-75711), Contia tenuis (AMNH R-69062), and Rhadinaea flavilata (AMNH R-50491) the right pituitary vein foramen is conspicuously larger than the left, a frequent asymmetry in colubroids related to a tendency to have blood enter the pituitary on the left (from the functional carotid) and leave on the right, through a large pituitary vein.

Eutrachelophis bassleri and E. steinbachi have very similar prootic bones, including the pattern of foramina in the region of the trigeminal and facial foramina. This pattern is imposed by the fusion of the alethinophidian bridge, or ‘‘Gaupp’s bone,’’ to the outer side of the prootic—external to branching of the trigeminal and to the petrosal sinus or network of veins around the trigeminal ganglion. The precise pattern of foramina depends on just where the edges of the alethinophidian bridge lie relative to a complex pattern of veins and nerves that cross one another. The pattern appears to be the same in the single skull each of Eutrachelophis bassleri and E. steinbachi , a remarkable coincidence if they are not closely related, particularly given that it was impossible to match this pattern with any of the other ‘‘xenodontine’’ (or other colubrid) skulls compared. In both Eutrachelophis bassleri and E. steinbachi , foramen V 2 for the maxillary nerve is broadly separated from foramen V 3 VII for the mandibular and facial nerves by the more dorsal portion of the alethinophidian bridge, as in Apostolepis , Oxyrhopus , Rhadinaea , and others; in Hydrops , Manolepis , Tantalophis , and others, the two foramina are closer together, and in some Heterodon (e.g., H. nasicus, AMNH R- 109431) the two foramina are confluent because of failure of the dorsal part of the alethinophidian bridge to extend between V 2 and V 3. Dorsal to the aperture for V 3, both have a small foramen opening posterodorsally, probably for the vein connecting the petrosal sinus with the main stem of the vena capitis lateralis. Urotheca multilineata (AMNH R-98288) has a similar foramen, but also another, probably venous, foramen just posterodorsal to the aperture for V 2. A venous (?) foramen posterodorsal to the V 2 aperture, but no venous foramen near the V 3 aperture, was found in Rhadinaea laureata (AMNH R-68380) and Thamnodynastes pallidus (AMNH R-4446); most of the ‘‘xenodontines’’ compared had no venous foramina dorsal to the apertures for V 2 and V 3. Ventral to the aperture for V 3, both Eutrachelophis bassleri and E. steinbachi have a small foramen facing downward and forward, probably for the palatine ramus of the facial nerve (VII pal.) just anterior to this foramen (and sharing a common longitudinal groove with it) is a small foramen facing downward and backward. To judge from dissection of Coniophanes quinquevittatus (AMNH R- 76693) this foramen is for the small trigeminal ramus to the protractor quadrati muscle (V 4 pro. quad.); dissection of Tantalophis discolor (AMNH R-103130) revealed two similarly placed foramina, but with the VII pal. foramen anterior to the V 4 pro. quad. foramen; since the two nerves cross in this region, just which foramen is the more anterior depends on precisely how far ventrally (i.e., to just above or to just below the crossing) the alethinophidian bridge extends. The direction the foramina face indicates that Eutrachelophis bassleri and E. steinbachi are more like Coniophanes than like Tantalophis in this aspect of the pattern.

Ventral to foramen V 2, Eutrachelophis steinbachi has a rather large foramen, but E. bassleri has a slightly larger foramen with a conspicuously smaller foramen immediately behind it; probably the larger foramen of E. bassleri is for the venous connection of the pituitary–middle cerebral vein to the petrosal sinus and the smaller foramen immediately behind it is for the retractor pterygoideus nerve (V 4 levator bulbi). The confluence of the two foramina in Eutrachelophis steinbachi is by far the more usual condition. Most ‘‘xenodontines’’ (apart from the anomalous Heterodon , whose foramina associated with the alethinophidian bridge are difficult to homologize with other snakes) have a V 4 levator bulbi foramen similar to that of Eutrachelophis steinbachi , but in Urotheca multilineata (AMNH R-98288) and Rhadinophanes the foramen is very small, suggesting it is for the nerve alone and the vein is absent, and, to judge from the size of the foramen, the vein must have been very small in Rhadinaea flavilata (AMNH R-50491) and Coniophanes fissidens (AMNH R-69977). In Pseudoeryx plicatilis (AMNH R-52229) the V 4 levator bulbi foramen is confluent with the aperture for V 2 and in Hydrops marti (AMNH R-52031) the V 4 levator bulbi foramen is anterior to, rather than below, the V 2 aperture.

In summary, the presence of venous (?) foramina dorsal to the trigeminal ganglion, together with the details of the pituitary vein foramen, contribute to the unusual pattern of the two Eutrachelophis skulls examined.

As in most ‘‘xenodontines,’’ both Eutrachelophis bassleri and E. steinbachi have a large and longitudinally oval footplate of the stapes that is overhung by a dorsal crista circumfenestralis, formed about equally by the prootic and exoccipital, and partially covered from below by the longissimus crest of the exoccipital, which conceals the recessus scalae tympani from lateral view. Although the skull of each was prepared from a male with well-mineralized hemipenial spines and with a strongly convoluted vas deferens (thus, presumably mature), in neither species does the dorsal crista circumfenestralis touch the longissimus crest to enclose the stapedial footplate entirely (such complete enclosure is uncommon in ‘‘xenodontines,’’ but occurs in Apostolepis flavotorquata, AMNH R-93559, Arrhyton taeniatum [see Maglio, 1970], Taeniophallus brevirostris, AMNH R-15207, and in Urotheca multilineata, AMNH R-98288). At the opposite extreme is Heterodon , where the stapes is almost entirely exposed to direct lateral view.

In both Eutrachelophis bassleri and E. steinbachi , the tabular (supratemporal or squamosal of some authors) is small and barely projects posteriorly beyond the sheath (in the exoccipital bone) of the posterior semicircular canal; anteriorly, it falls well short of the parietal bone, but, nevertheless, it is exposed anterior to its contact with the quadrate and is about equal in length to the quadrate. Thus, the reduction of the tabular, which results in the suspension of the quadrate lying opposite, rather than behind, the rear of the otic capsule, is more as in Apostolepis , Atractus , and Carphophis , than as in Dipsas and Sibon . As in other ‘‘xenodontines’’ (but unlike genera such as Boaedon , Elapoidis , Lycophidion , and Psammodynastes ), the lateral margin of the tabular is gently sinuate, without a distinct and angular lateral lobe extending onto the dorsal crista circumfenestralis. Further, as in most ‘‘xenodontines’’ (even those, such as Oxyrhopus and Thamnodynastes , with a strong backward extension of the tabular), there is no tubercle or ridge or countersinking of the cranial surface for the tabular and that bone would seem to have a slight mobility in its cranial attachment. Hence, since the quadrate makes no direct contact with the cranium, some slight adjustment in the angle of rotation of the quadrate (relative to the cranium) seems possible, although the lack of backward projection of the tabular would make the leverage for this adjustment very small in the case of Eutrachelophis bassleri and E. steinbachi . In genera with an angular notch in the lateral border of the tabular (such as Psammodynastes and Lycophidion ), a tubercle of the prootic fits into this notch and locks the tabular into position. In contrast, the xenodontine Oxyrhopus (as noted during preparation of the skull of O. petola, AMNH R-52640), although having a long tabular projecting well behind its contact with the cranium, has the tabular held in position by ‘‘guy wires;’’ that is, strong ligaments, one from the nuchal crest of the supraoccipital to the medial edge of the tabular and another from a longitudinal ridge on the prootic to the lateral edge of the tabular, hold the tabular in place. A few ‘‘xenodontines’’ seem to have a rigidly locked tabular: in Heterodon platyrhinos (AMNH R-63590), the surface of the prootic for the tabular is corrugated, and in Apostolepis flavotorquata (AMNH R-93559), the tabular is strongly S-shaped, with an irregular outline that fits a countersunk depression on the exoccipital behind the crista circumfenestralis.

The quadrate is of similar triangular form in Eutrachelophis bassleri and E. steinbachi , but less backswept in the latter; in both, the stapedial facet (processus internus module) is at almost the exact center of the posterior profile of the bone, rather than conspicuously ventral to the center (as in Farancia ) or distinctly above the center (as in Rhadinaea decorata, AMNH R-107588).

Both Eutrachelophis bassleri and E. steinbachi have the most common form of occipital condyle among ‘‘xenodontines’’ and other colubrids: conspicuously narrower than the foramen magnum, but transversely oval in form, with the exoccipitals well separated by the basioccipital, and without distinct peduncle or neck; in some ‘‘xenodontines,’’ such as Farancia abacura (AMNH R-110941) and Carphophis amoenus (AMNH R-121650) the condyle may be much broader, as broad as the foramen magnum; in others, such as Apostolepis flavotorquata (AMNH R- 93559) and Pseudoeryx plicatilis (AMNH R- 52229), the condyle is distinctly pedunculate and the exoccipitals meet above the basioccipital.

COLOR PATTERN

The color pattern of snakes can be as useful in phylogenetic studies as it is in identification, but authors tend to yield precedence when conflicting hemipenial data are involved. For example, the sister genera Pliocercus and Urotheca (the latter equivalent to the former lateristriga group of Rhadinaea ) share the characters of a long, disproportionately thick tail and a hemipenis having a small, naked pocket in the asulcate edge of the capitulum ( Myers, 1974: 273, fig. 4). On this basis, Savage and Crother (1989) united the two genera. Myers and Cadle (1994: 3) disagreed with that action, saying that:

Present evidence suggests that Pliocercus and Urotheca s.s. are monophyletic sister groups— each of which is characterized by synapomorphies of color pattern, including Micrurus -like rings in the former and a longitudinal white line(s) [sometimes secondarily lost] in the latter. … there is no indication that Urotheca s.s. is paraphyletic with respect to Pliocercus . Inasmuch as the evolutionary history of Pliocercus is linked via mimicry complexes with venomous coral snakes … we prefer to regard it and Urotheca s.s. as evolutionarily distinct sister genera.

One wonders whether ‘‘mimicry’’ of a sort might also have been involved in the evolutionary development of the distinctive color pattern of Eutrachelophis . This pattern includes striking dark-rimmed whitish ocelli or elongated spots on the head, or head and neck, with a weak semblance of dorsal dark spots/stripes anteriorly, becoming nearly uniform posteriorly. See figures 1–2 and 4–8 in the species accounts. There is both inter- and intraspecific variation in the alignment of the pale ocellar markings, but the variation seems relatively minor and the combined patterns seem to us diagnostic at the generic level. Eutrachelophis bassleri and E. steinbachi differ from one another in the alignment of their postocular and nuchal markings (compare figs. 2 and 8)—but this minor variation is in total greatly exceeded in the similar markings of Rhadinaea decorata , as portrayed in Myers (1974: fig. 15A–E).

Although the head and nuchal patterns in Rhadinaea decorata include all the variants seen in the combined head and neck patterns of Eutrachelophis spp. , parts of the overall color pattern of Eutrachelophis are shared with other snakes as well. The overall appearance of the head and neck pattern is reminiscent, for example, of Amnesteophis melanauchen (fig. 13A, B) and Tantilla melanocephala (fig. 13C). The pattern is intraspecifically variable in the last species and probably in the first (known from a single specimen). In figure 13 an anterior band or spots (first arrow) are followed by paired spots or a fused pale crossbar (second arrow) that is medially constricted like the fused ocelli in some specimens of Eutrachelophis (compare with figs. 2 and 4).

Postparietal and nuchal ocellar markings appear in Rhadinaea and other genera of ‘‘ Rhadinaea -like snakes,’’ 14 but only in a few, such as Echinanthera undulata , are they as conspicuous to the human eye as in Eutrachelophis (fig. 14A). More often, as in species of Taeniophallus , the markings represent the anterior terminus of a stripe or other body

14 ‘‘The Rhadinaea -like snakes are mainly tropical species of similar habits and habitus—terrestrial in forest, usually diurnal (always with round pupils), small and slender, often striped, and with a generalized colubrid morphology’’ ( Schargel et al., 2005: 12). They include but are not limited to genera recently removed from Rhadinaea (i.e., Rhadinella , Taeniophallus , Urotheca ; see Myers, 2011: 26–19). Some Old World snakes also are Rhadinaea -like in the above sense, as pointed out by Cadle (1996a: 374) when he named the new Liopholidophis rhadinaea from Madagascar; the males of this species have extraordinarily long tails, but SVL of males and total lengths of females are comparable to many Rhadinaea . Although species of Rhadinaea generally are smaller, more delicate snakes, R. taeniata approaches some Liopholidophis in size.

+

snake that is known only from the type specimen collected in or at ‘‘Bahia’’ prior to 1863 (reproduced from Myers, 2011). C. Tantilla melanocephala (Linnaeus) . AMNH R-101970 from Amazonas, Manjuru River (4 ° S, 57 ° W). Head and nuchal patterns probably are intraspecifically variable in all. color (fig. 14B) or simply the anteriormost of a series of similar spots (fig. 15A). On the other hand, a distinct white canthal-postocular line occurs in different species of Rhadinaea and Taeniophallus but seems absent in the variational repertory of Eutrachelophis . Some of these snakes, such as Taeniophallus bilineatus (fig. 14B), share with Eutrachelophis a lateral line of whitish dashes emphasized by black edging, found on row 4 in E. bassleri (fig. 1A) and row 6 in E. steinbachi (figs. 5, 6), although these lines are nonhomologous (being edging to a dark lateral stripe in steinbachi ). Similar species-specific differences in positioning of this line of pale dashes (and the black edging, which may show as a continuous narrow stripe) also occur in other genera (e.g., the decorata group of Rhadinaea ).

GENERALITIES BASED ON EUTRACHELO- PHIS -LIKE COLOR PATTERNS: A few correlations based on this section seem of interest. First, all the examples given are of little serpents that are mostly (entirely?) inhabitants of leaf litter in humid forest. All are small, relatively slender snakes with usually smooth dorsal scales (some weakly keeled in Amnesteophis ), usually in 15 rows or 17 rows in a few. Of particular interest is the variation usually present in the head and nuchal color patterns of clearly unrelated species. These patterns seem exceptionally variable within species. There is little or no evidence showing the patterns to be strongly constrained by natural selection—leading to the notion that selection may actually favor the variability, especially of ocellar markings. (Reader: construct your own explanatory scenario.) Neck ‘‘rings’’ (simple collarlike markings) seem somewhat less variable within species, the best example being perhaps the familiar, geographically widespread North American ring-necked snakes ( Diadophis ); even in this genus, however, the neck ring is sometimes broken or even absent. Color patterns of the head and neck may have potential for active evolutionary change in small leaf-litter snakes.

HEMIPENES

Eutrachelophis bassleri has an extremely unusual hemipenis when compared with ‘‘colubrid’’ and ‘‘xenodontine’’ snakes generally. E. bassleri originally was thought to be a species of Leimadophis (now 5 Liophis ), although that was ruled out once the hemipenis and its retractor muscle were seen to be unbifurcated. Nonetheless, from the appearance of the distal nude section of the retracted hemipenis (fig. 3A), it still seemed possible that it might evert as a large flattened or centrally depressed apical disc. If that were the case, it might somehow support a relationship with the Xenodontini (which have apical discs on bifurcated hemipenes). Instead, the E. bassleri organ everted with a domelike head or capitulum (fig. 3B– D). 15 Although there are some similarities with the hemipenis of its unnamed sister species (fig. 4 and associated text), we have seen nothing quite like the hemipenis of E. bassleri among Neotropical snakes. A resemblance to the general physiognomy of the bassleri hemipenis is found in the Malagasy Compsophis infralineatus , as shown in figure 21; this species also has a pronounced hemipenial head or capitulum without being capitate.

On the other hand, although the deeply divided hemipenis of Eutrachelophis steinbachi (fig. 9) is markedly different from, E. bassleri , it has parallels in other taxa. Genera with similarly long-lobed hemipenes include the South American Xenodon suspectus , X. rabdocephalus , and the African, Mehelya poensis , all to be discussed and illustrated later.

Consideration of such differences might begin with the concept of a ‘‘random walk’’ (sensu Raup and Gould, 1966). 16 The analogy

15 This hemipenis is not ‘‘capitate’’ in the usual sense because the capitulum lacks ‘‘a free overhanging edge’’ ( Myers, 1974: 31) or ‘‘capitular groove’’ (Zaher, 1999: 9).

16 Raup and Gould (1966) give an idea of how much similarity might be produced by random computer changes in morphology. A punctuated equilibrium model was imposed that did not allow phyletic change in the ancestral species and permitted ‘‘morphological change’’ only in association with the speciation process. Interspecific evolutionary effects and adaptation to unexploited niches were intentionally omitted, since one purpose was to determine how much of the pattern usually interpreted as adaptation to coexistence of species could be produced by chance.

The characters generated in Raup and Gould’s simulation of ‘‘morphology’’ are not comparable to ‘‘morphological characters’’ as used by most herpetologists, but are more analogous to growth rates, +

tissue differentiation rates, cell migration rates, hormone production rates, hormone response rates, etc.; that is, the analogy is to quantitatively variable developmental processes. Taxonomists prefer ‘‘characters’’ that are binary and Raup and Gould’s simulation does not describe the way taxonomists like to use ‘‘characters.’’ Their simulation reflects Raup’s (1966) virtuoso performance in explaining most of the morphology of snail shells by three independent growth rates.

Therefore, a vertebrate taxonomist can take little comfort from Raup and Gould’s ability to recover most ‘‘phylogeny’’ from the ‘‘morphology’’ of their ‘‘species.’’ +

This ‘‘morphology’’ was relatively well known, since each generating ‘‘growth rate’’ was known. Yet, with this perfect knowledge of the determiners of form, Raup and Gould could obtain only a close, but imperfect, reconstruction of the ‘‘phylogeny.’’ Their simulation of a phylogeny with morphological change was a random walk model, and. as they discuss, it did not produce a general convergence of all ‘‘phyletic lineages’’ on some average morphology. Instead, various ‘‘lineages’’ acquired distinctive ‘‘morphologies’’ and a recognizable suite of ‘‘morphological characters’’ (at least for their clade 91, discussed and figured with some detail). between a random walk and what appears to be the phylogeny of colubrids is striking. The analogy is particularly apparent when Eutrachelophis bassleri , E. steinbachi , and other ‘‘xenodontines’’ are compared with the colubrids of Madagascar. One Madagascan colubrid, Mimophis , differs from other Madagascan forms, as well as from all ‘‘xenodontines,’’ in the greatly reduced hemipenis; it is a psammophiid and seemingly represents an independent Madagascan invasion separate from other colubrids ( Cadle, 2003; Nagy et al., 2003; Kelly et al., 2008). Putting aside Mimophis , all the other Madagascan colubrids represent a monophyletic clade (Pseudoxyrhophiinae), all members of which differ from Eutrachelophis bassleri and E. steinbachi in the presence of strong hypapophyses on the posterior vertebrae, even though these two Neotropical snakes agree with all Madagascan colubrids in lack of hemipenial calyces and show a particular resemblance to Thamnosophis lateralis (but not to Liopholidophis sexlineatus ) and to Dromicodryas in the construction of the orbital region of the skull. Although lack of posterior hypapophyses distinguishes many ‘‘xenodontines’’ from Madagascan colubrids that resemble them (e.g., the xenodontine Liophis and the Madagascar Liopholidophis ), it is not absolutely diagnostic, since some ‘‘xenodontines’’ (e.g., Amastridium , Ninia , Nothopsis ) have posterior hypapophyses, but these ‘‘xenodontines’’ with hypapophyses do not happen to have any counterpart in Madagascar that resembles them (the ‘‘xenodontines’’ mentioned have hemipenial calyces, for example). Even though the Madagascan Thamnosophis lateralis is more like Eutrachelophis steinbachi than it is like the Madagascan Liopholidophis sexlineatus in construction of the orbit, and also in the maxillary dentition with a broad diastema anterior to the enlarged last pair of teeth and in the terminal expansion of the parasphenoid, it differs from Eutrachelophis steinbachi and resembles Liopholidophis sexlineatus in a feature of the hemipenis: the organ forks only a short distance distal to the furcation of the sulcus, whereas in Eutrachelophis steinbachi the sulcus forks near the base of the organ, while the organ itself forks well distal to this, and in Eutrachelophis bassleri the unforked organ ends far distant from the sulcus furcation. But this hemipenial difference fails when we compare Eutrachelophis steinbachi with Dromicodryas (probably closely related to Thamnosophis lateralis , and with a similar orbit and with a distinctly expanded tip of the parasphenoid [expanded and also forked in the specimen illustrated by Cadle, 1996a: fig. 39, bottom]), since Dromicodryas also has the furcation of the sulcus far proximal to the terminal bilobation of the organ. However, Dromicodryas is not a ‘‘morphological intermediate,’’ since its maxillary dentition lacks posterior enlarged teeth and diastema (thus suggesting the Madagascan Liophidium and Micropisthodon , which it also resembles in having a reduced splenial bone, but these genera have the sulcus furcation near the furcation of the organ).

In spite of a search involving details of the skull, lungs, hemipenial morphology, and head muscles, no character has emerged that will distinguish all Madagascan colubrids from all ‘‘xenodontines.’’ This is precisely what would be expected if both the Madagascan radiation and the ‘‘xenodontine’’ radiation represent random walks with similar rules for morphological change. The same characters might easily arise here and there in both radiations, but for the same character combinations to arise in both radiations would be quite improbable.

Even without taking the comparisons to Madagascar, the question remains: How can one conceive Eutrachelophis bassleri and E. steinbachi as congeners when they have such markedly different hemipenes? We explore this question further in the Discussion below. See also the Commentary on Hemipenes as Generic and Specific Characters.

SUMMARY OF GLOBAL COMPARISONS

Various details have been noted in the preceding anatomical and color comparisons; few of these details need be considered important in themselves, since they involve characters known to vary among ‘‘xenodontine’’ snakes. However, as summarized here, some shared traits are rare or uncommon and, in total, these appear indicative of close relationship between Eutrachelophis bassleri and E. steinbachi .

VISCERA AND HEAD GLANDS: Characters of the viscera are widely shared and provide nothing of special interest. Among features of the head glands, both species (1) show an unusually large temporal extension of the Harderian gland; and (2) lack evidence of a rictal gland (sensu McDowell, 1986). Finally, (3) both species, plus the unnamed sister species of E. bassleri , have a well-differentiated, similarly positioned ‘‘supralabial gland,’’ the outline of which can easily be seen through the postorbital supralabial integument in some preserved specimens (fig. 4). The serous (Duvernoy’s) portion of this gland is not clearly differentiated (to gross examination) from the mucous part of the gland, and enlargement of the rear maxillary teeth is not accompanied by a correspondingly conspicuous differentiation of the gland.

HEAD MUSCLES: (1) Both Eutrachelophis bassleri and E. steinbachi have unusually weak jaw muscles and neither species is well adapted to engulfing relatively large prey while exerting much force. (2) The levator anguli oris of both species is converted into a compressor of the Harderian gland; only the more posterior fibers of this muscle are retained, with only those originating on the parietal being present; no fibers originate on the postorbital and none extend to the corner of the mouth or curve forward beneath the corner. (3) The insertion pattern of the retractor arcus palatini in both bassleri and steinbachi is the pattern that is most common among colubrids, but in both species this muscle is unusually slender, its origin from the sphenoid being slightly narrower than the origin of the retractor vomeris (also on the sphenoid). In most New and Old World colubrids, the retractor arcus palatini is at least slightly larger, usually conspicuously larger, than the retractor vomeris.

SKULL AND DENTITION: (1) The skulls of E. bassleri and E. steinbachi have an unusually short tabular, such as seen in some small-eyed burrowers, but it is combined with a construction of the orbit associated with largeeyed snakes. (2) When details of foramina of the sphenoid and prootic are considered, there is a virtual identity between the two skulls, even though the foramina are so labile that closely related snakes, or even the left and right sides of the same skull, may differ. The only significant skull difference between the two is that E. steinbachi has a dorsal crest of the parasphenoid rostrum that is lacking in E. bassleri . (3) The presence of venous (?) foramina dorsal to the trigeminal ganglion, together with the details of the pituitary vein foramen, result in an exceptional pattern not duplicated in any other ‘‘xenodontine’’ examined. (4) The dentition and shapes of the dentigerous bones show a near identity in E. bassleri and E. steinbachi . Also to be included is the form of the ectopterygoid, which is so easily modified that differences often are seen between closely related species; both species agree in having a long (for Colubroidea) retroarticular process.

COLOR PATTERN: The distinctive color pattern of Eutrachelophis includes striking dark-rimmed whitish ocelli or elongated spots on the head and neck, with a weak semblance of dorsal dark spots/stripes anteriorly, becoming nearly uniform posteriorly. Eutrachelophis bassleri and E. steinbachi differ from one another mainly in the species-specific alignment of the postocular and nuchal markings (this variation is in total exceeded by similar markings of Rhadinaea decorata ). As discussed, other small leaf-litter snakes share elements of the Eutrachelophis color pattern and some also have 15 rows of smooth dorsal scales, but none is likely to be mistaken for Eutrachelophis and all differ fundamentally in features of dentition and hemipenes.

Figures

Fig. 4. Eutrachelophis species (MZUSP 10530, head in dorsal and lateral view; a female from Cabeceira do Rio Urucu, central Amazonian Brazil). This unnamed snake appears to be the sister species of E. bassleri. See Remarks and compare with figure 2. Formalin preservation caused the integument of this specimen to become slightly translucent, giving visibility to a large ‘‘supralabial’’ gland (SG); this large gland (similarly positioned in all three species of Eutrachelophis) is adherent to the medial side of the supralabial integument. The mucous and serous (Duvernoy’s) parts of the gland cannot be distinguished in Eutrachelophis without histological examination.

Fig. 5. Eutrachelophis steinbachi (Boulenger). Adult female shown approximately life size (BMNH

Fig. 6. Eutrachelophis steinbachi (Boulenger). The paralectotype (BMNH 1946.1.21.63), a juvenile male shown 1.6× life size.

Fig. 7. Eutrachelophis steinbachi (Boulenger), handheld preserved specimens. Upper. A specimen (NMW 23106) cited as ‘‘syntypus’’ by Tiedemann and Häupl (1980: 61) but not mentioned in Boulenger’s (1905: 454) original description. Low- er. The syntype (BMNH 1946.1.21.63) designated lectotype in this paper (photograph courtesy of James R. Dixon).

Fig. 8. Head of Eutrachelophis steinbachi (Boulenger) (UMMZ 60736), showing details of color pattern. The oblique alignment of the pale ocelli differentiates E. steinbachi from E. bassleri and its unnamed sister species (cf. figs. 2 and 4).

Fig. 9. Uneverted hemipenis of Eutrachelophis steinbachi (Boulenger); right organ of AMNH R-125695, opened by midventral incision, ×5. Abbreviation: STB, smooth terminal basin.

Fig. 11. Skull of Eutrachelophis steinbachi (Boulenger) (AMNH R-125695), ×7.7. Abbreviations: Same as for figure 10, but here repeated only for nerve and venous foramina. With only one skull each of E. bassleri and E. steinbachi, no significance can be attached to any slight differences in positioning of these foramina, which are so labile that even the left and right sides of the same skull may sometimes differ.

Fig. 12. Maxillary dentition of Eutrachelophis steinbachi (Boulenger). Right maxilla of AMNH R- 125695, in lateral and ventral view. Arrangement of tooth sockets shows a slight lateral offset of the last tooth behind the diastema; the offset is more pronounced in most other ‘‘xenodontines,’’ although a few genera have the posterior maxillary teeth arranged in a straight line configuration.