Prionocyclus pluricostatus, KENNEDY & COBBAN & LANDMAN, 2001

KENNEDY, W. JAMES, COBBAN, WILLIAM A. & LANDMAN, NEIL H., 2001, A Revision Of The Turonian Members Of The Ammonite Subfamily Collignoniceratinae From The United States Western Interior And Gulf Coast, Bulletin of the American Museum of Natural History 2001 (267), pp. 1-148 : 81-139

(= Germariceras Breistroffer, 1947 )

TYPE SPECIES: Prionocyclus serratocarinatus Meek, 1871: 298 , non Stoliczka, 1865: pl. 32, fig. 31, = Prionocyclus wyomingensis Meek, 1876a: 452 .

DIAGNOSIS: Medium to large, adult up to 300 mm in diameter. Size­related dimorphism not recognized (due to paucity of adults), but the middle growth stages of all species occur as involute, relatively compressed, feebly ornamented gracile forms or more evolute, less compressed, strongly ornamented, robust forms. Ornament highly variable, typically of stronger primary ribs with umbilical, inner, and outer ventrolateral tubercles at some stage in ontogeny separat­ ed by weaker nonbullate and intercalated ribs that have inner and outer ventrolateral tubercles at some stage in ontogeny. Outer ventrolateral tubercles may decline or not, inner ventrolateral tubercles may bear long septate spines; faint inner lateral tubercles may develop during later growth stages. Siphonal keel is strong to weak, and finely serrated, with the number of serrations exceeding the number of ribs.

DISCUSSION: The type species of Prionocyclus and Collignoniceras are distinct, especially in the adult stage, and juveniles can be separated because the keel of Collignoniceras has siphonal clavi equal in number to that of the ventrolateral tubercles, whereas in Prionocyclus the serrations greatly outnumber the ribs (compare figs. 17, 18 and figs. 78, 84). In Prionocyclus , the marked differentiation of ribbing present in the early ontogenetic stages of certain variants of C. praecox (e.g., fig. 41F–U) persists to maturity.

Germariceras Breistroffer, 1947 (unpaged), with Ammonites germari Reuss, 1845 (fig. 109K), from the upper Turonian of Czech Republic as type species, is best known from the lithographs of Fritsch (1872: pl. 14, figs. 1, 2; pl. 16, fig. 7), and was recently revised by Kaplan (1988). It is here shown to be common and widespread in the U.S. Western Interior, and shows no characters that merit separation from Prionocyclus .

OCCURRENCE: Middle Turonian of the U.S. Western Interior, Gulf Coast, and northern Mexico; upper Turonian of the U.S. Western Interior, Gulf Coast, and northern Mexico, Tunisia, Japan, Czech Republic, Germany, and Kazakhstan. Records from Southeast France (Middlemiss and Moullade, 1968) are unsubstantiated.

Prionocyclus hyatti (Stanton, 1894) Figures 50–60

Prionotropis hyatti Stanton, 1894: 176 , pl. 42, figs. 5–8.

Prionocyclus hyatti Stanton. Logan, 1898: 468 , pl. 102, figs. 5–8.

Prionocyclus hyatti Stanton. Grabau and Shimer, 1910: 228 , fig. 1509e–g.

Prionocyclus hyatti Stanton. Diener, 1925: 156 .

Prionotropis aff. woollgari (Mantell) . Moreman, 1927: 97 (pars), pl. 13, fig. 2.

Prionotropis aff. P. hyatti Stanton. Adkins, 1928: 250 .

Prionotropis eaglensis Adkins, 1928: 250 , pl. 32, figs. 1, 2.

Pseudaspidoceras eaglense (Adkins) . Adkins, 1931: 53.

Prionotropis graysonensis (Shumard) . Moreman, 1942: 213.

Prionocyclus aff. woollgari Meek (not Mantell). Moreman, 1942: 214.

Prionotropis woollgari Meek (? non Mantell). Haas, 1946: fig. 45.

Collignoniceras hyatti (Stanton) . Cobban, 1951: 2188, 2191, 2192, fig. 2.

Collignoniceras hyatti (Stanton) . Cobban and Reeside, 1952: 1018.

Collignoniceras hyatti (Stanton) . Cobban, 1955: 204, pl. 2, fig. 10.

Collignoniceras hyatti (Stanton) . Hattin, 1962: 79, pl. 24, figs. A–E.

Prionocyclus hyatti (Stanton) . Powell, 1963: 1220, pl. 166, figs. 1, 8–12; text­fig. 5a, c, d, f–h.

Collignoniceras hyatti (Stanton) . Hattin, 1965: fig. 4 (4).

Prionocyclus hyatti (Stanton) . Matsumoto, 1965: 19, pl. 17, fig. 3.

Prionocyclus hyatti (Stanton) . Cobban, 1976: 122, pl. 1, fig. 1.

Prionocyclus hyatti (Stanton) . Kennedy and Cobban, 1976: pl. 8, fig. 3.

Prionocyclus hyatti (Stanton) . Kauffman, 1977: pl. 22, fig. 1; pl. 26, fig. 7.

Prionocyclus hyatti (Stanton) . Hattin, 1977: figs. 8 (9, 11).

Prionocyclus hyatti (Stanton) . Hattin and Siemers, 1978: fig. 10.

Prionocyclus hyatti (Stanton) . Kauffman et al., 1978: pl. 5, fig. 1.

Prionocyclus hyatti (Stanton) . Young and Powell, 1978: pl. 1, figs. 1–3, 7, 8.

Prionocyclus hyatti (Stanton) . Merewether et al., 1979: pl. 3, figs. 1, 2.

Prionocyclus hyatti (Stanton) . Cobban, 1984a: 85.

Prionocyclus hyatti (Stanton) . Cobban, 1986: fig. 3Q.

Prionocyclus hyatti (Stanton) . Kennedy, 1988: 75, pl. 15, figs. 1–24; pl. 16, figs. 1–20; pl. 17, figs. 1–7; text figs. 24d, e, f, 25–27, 31b.

Prionocyclus hyatti (Stanton, 1894) . Kennedy and Cobban, 1988: 606, figs. 7. 1–8, 11.

Prionocyclus hyatti (Stanton, 1894) . Kennedy et al., 1989: 89, figs. 24f, g, m, 25, 26a, b, 27a–j, s–w.

Prionocyclus hyatti (Stanton) . Cobban and Hook, 1989: fig. 9i, j.

Prionocyclus hyatti (Stanton) . Cobban, 1990: pl. 5, figs. 3–5.

Prionocyclus hyatti (Stanton, 1894) . Emerson et al., 1994: 210, unnumbered figures on pp. 210, 211.

Prionocyclus hyatti Stanton, 1893 . Kirkland, 1996: 99, pl. 50, figs. L, M.

Prionocyclus hyatti (Stanton, 1894) . Reyment and Kennedy, 2001; fig. 2a–d.

TYPES: Lectotype, by subsequent designation of Matsumoto 1965: 19, is USNM 22941 , the original of Stanton’s 1894: plate 42, figures 5, 6 (fig. 50C–E); figured paralectotype is USNM 22941 a, the original of Stanton’s plate 42, figures 7, 8 (fig. 50A, B). They are from the Codell Sandstone (Pugnellus Sandstone) of Williams Creek and Poison Canyon , Huerfano Park , Colorado. Stanton refers to many specimens from Huerfano Park and a few from Coalville , Utah: all are paralectotypes (e.g., fig. 50F– H).

DIAGNOSIS: A moderately evolute fairly large species ornamented by straight, prorsiradiate primary and secondary ribs terminating in ventrolateral tubercles. Low keel differentiated into low asymmetric clavi slightly more numerous than the ribs. Inner whorls usually densely ribbed. Primary ribs on outer whorl support umbilical bullae or nodate umbilical tubercles. Inner ventrolateral tubercles on adult body chamber may enlarge into conspicuous spines.

DESCRIPTION: The lectotype is a small, robust specimen (Stanton, 1894: pl. 42, figs. 5, 6; Matsumoto, 1965: 19, pl. 17, fig. 3a–c; fig. 50C–E). Measurements in millimeters and ratios from a plaster cast are as follows: D = 31.0, Wb = 14.2 (46%), Wh = 12.0 (39%), Wb:Wh = 1.18, U = 10.6 (34%). Primary and secondary ribs arise on the umbilical wall and are straight and prorsiradiate on crossing the flanks. They number 29 per whorl at a diameter of approximately 7.5 mm, and 29 per whorl at a diameter of about 19 mm. Primary ribs support umbilical bullae, prominent clavate inner ventrolateral tubercles, and weak outer ventrolateral clavi. Some secondaries bear weaker ventrolateral tubercles. All ribs bend forward on the ventrolateral shoulder and fade out at an angle toward the keel. Most primaries and secondaries alternate. Toward the adapertural end, the inner ventrolateral tubercles on the primary ribs enlarge and become hornlike, projecting outward at a low angle to the venter. In this manner, the specimen is much like the last part of the phragmocone of the remarkable spined individual figured by Kennedy and Cobban (1976, pl. 8, fig. 1; fig. 58) from the Carlile Shale of Kansas. On the older part of the outer whorl of Stanton’s specimen, the keel is differentiated into low clavi that correspond to the ribs, but on the younger part, the clavi seem to number about two per rib.

The other specimen figured by Stanton (1894: pl. 42, fig. 7; fig. 50A, B) is a small, gracile, evolute specimen 21.0 mm in diameter with an umbilical ratio of 49% (measurements from a plaster cast). The keel is low and appears to be differentiated into asymmetric clavi that are less numerous than the ribs. Ribs are narrow and prorsiradiate; they number 35 on the outer whorl, where one or two secondaries separate primaries.

In the lower, Hoplitoides sandovalensis Subzone of the Prionocyclus hyatti Zone , a collection from a narrow horizon in the Semilla Sandstone Member of the Mancos Shale at USGS locality 28873 (locality 41 in fig. 1) is typical. It and other collections reveal that both robust and gracile forms are present in similar numbers.

In the robust form (figs. 55C, D, 56–58), nuclei show great variation. Coiling is very evolute, with the umbilical seam indented to accommodate the inner ventrolateral tubercles of the inner whorl, the umbilicus is of moderate depth, the umbilical wall flattened and subvertical, the umbilical shoulder quite narrowly rounded, the whorls slightly compressed to depressed, quadrate in intercostal section, and octagonal in costal section (table 7). At one extreme there are as few as 20 ribs per whorl, with up to 30 at the other. The ribs are all bullate primaries of equal development, strong, straight, and prorsiradiate, and strengthen across the flanks to strong conical to clavate inner ventrolateral tubercles. A broad prorsiradiate rib connects an inner ventrolateral tubercle to a strong outer ventrolateral clavus, and a smooth zone separates the ribs from a strong siphonal keel, with clavi occupying the interspaces between tubercles (fig. 56C–D). As size increases, the ribs become very coarse and massive, with strong (fig. 56H–J) to weak bullae (fig. 56C, D), with as few as 16 ribs per whorl. Sometimes the bullae are of variable strength (fig. 56E–G), and displaced out from the umbilical shoulder. The outer ventrolateral clavi are assimilated into the inner ventrolateral tubercles, which enlarge into massive blunt horns that project outward but usually not significantly above the level of the venter (fig. 56E–J). Other robust individuals have nuclei in which strong, bullate primary ribs are separated by up to three weaker nonbullate primaries, with a total of up to 45 ribs per whorl. This differentiation persists into middle growth. The bullate primaries have strong umbilical bullae and inner and outer ventrolateral tubercles. The nonbullate primaries sometimes connect to the umbilical bullae as mere striae and have weak ventrolateral tubercles, in some cases, only outer ones. In some specimens (fig. 58) the stronger primaries develop massive horns or spines, with hornless ribs between. The largest robust individual at hand is 270 mm in diameter.

Nuclei of the gracile form (figs. 51A–R, V–Y, 52A–L, 53, 54, 55E–J) overlap to a degree with those of the robust form. They are more compressed, with a broad, shallow umbilicus (table 7), and have up to 50 ribs per whorl that may be even (fig. 51M–O) or vary greatly in strength (fig. 51A–I). The stronger ribs are flared, usually bullate, with inner and outer ventrolateral tubercles; the weaker ribs lack bullae and have feeble or no inner ventrolateral tubercles. This style of ornament may persist into middle growth, and there are gracile forms with dense, even ribs that may reduce to mere striae (fig. 51N) and others with ribbing of variable strength and tubercle development (fig. 52K, L). Inner and outer ventrolateral tubercles remain separate and do not merge into horns, as in the robust form; nonbullate ribs may lack an inner ventrolateral tubercle and have much weaker outer ventrolateral tubercles than on the bullate primaries. The keel is broadly and irregularly undulose.

Both robust and gracile forms show enormous variation in ribbing and tuberculation style as well as timing of ontogenetic changes in ornament. This is more readily appreciated from the illustrations (figs. 50–60) than from mere description.

Prionocyclus hyatti from the upper part of its zonal range is illustrated by collections from the Carlile Shale of Kansas, where the species occurs as fragments, often of large body chambers, in ironstone concretions. Original aragonite shell is often preserved (fig. 57). Many of the specimens we have seen from Kansas are large, up to 300 mm in diameter. Juveniles are as variable as those from the Hoplitoides sandovalensis Subzone in New Mexico and elsewhere already described, with even, coarse to fine ribbing as well as markedly differentiated weak and

TABLE 8 Dimensions of juvenile Prionocyclus macombi Meek, 1876 a

strong ribs. This variation is maintained into middle growth, and most individuals have strong, bullate primary ribs with massive ventrolateral horns and weaker, nonbullate intercalated ribs between that have weak ventrolateral tubercles. At the largest diameters, fragments may bear as few as six ribs with massive ventrolateral horns per half whorl, and some specimens show the horns to have been septate, with a long spine (fig. 59).

These large specimens commonly show an outward migration of the umbilical bullae, which become conical and occupy an inner flank position. The keel of these specimens is variable, from broadly undulose with coarse clavi only slightly more numerous than ventrolateral tubercles (fig. 57A, B) to others where the crenulations are minute and far more numerous.

The suture (fig. 60) has moderately incised elements; E/L is broad and bifid, and L is narrower and bifid, as is L/U 2.

DISCUSSION: Prionocyclus hyatti is the species of the genus closest to Collignoniceras , discussed above. Juvenile stages show certain common characters, but middle and late growth stages are distinct. Prionocyclus hyatti differs from the most closely comparable Prionocyclus , P. macombi , as follows: the robust forms of the two species may have a degree of overlap in their coiling, whorl section, and expansion rate, but small and mediumsized individuals of P. macombi never develop ventrolateral horns as massive as those of P. hyatti , nor the striking differentiation into strong horned ribs with umbilical bullae, and weak, nonbullate hornless ribs. The gracile forms of P. macombi are much more compressed, higher­whorled, and more involute than the corresponding forms of P. hyatti . The

TABLE 9 Dimensions of Prionocyclus macombi Meek, 1876 a

ribbing is also denser and finer in P. macombi with the ribs often reduced to mere striae, and the inner and outer ventrolateral tubercles of the inner whorls replaced by a single ventrolateral clavus at an early stage.

OCCURRENCE: Widely distributed in the Western Interior from northern Montana southward into Trans­Pecos Texas and eastward from there into central and northern Texas (fig. 61). Also known from northern Chihuahua, Mexico, and Kazakhstan (Marcinowski et al., 1996).

Prionocyclus albinus (Fritsch, 1872) Figures 62 , 108C

Ammonites albinus Fritsch, 1872: 28 , pl. 6, fig. 4.

Ammonites albinus Fritsch. Diener, 1925: 23 .

Prionocyclus hyatti (Stanton, 1894) . Kennedy, 1988: 75 (pars), pl. 15, figs. 3–5; text­fig. 25H–L only.

TYPE: Lectotype, here designated, is the original of Fritsch , 1872: plate 6, figure 4, no. 03144 in the Collections of the Narodni Museum, Prague, from the Turonian of Wehlovice, in the Czech Republic (fig. 108C is a plaster cast taken from an external mold of the type).

DIAGNOSIS: A moderate­sized, fairly evolute species that has whorls higher than wide with flattened flanks. Ornament of numerous prorsiradiate ribs with primaries usually separated by two or three secondaries.

DESCRIPTION: The lectotype is 41 mm in diameter. Coiling is evolute, with U/D = 0.42. The umbilicus is shallow, with a feebly convex wall, and more narrowly rounded umbilical shoulder. On the last half whorl, six or seven primary ribs arise on the umbilical wall, and strengthen into feeble bullae perched on the umbilical shoulder. The ribs are coarse, straight, and prorsiradiate on the flanks, with inner and outer ventrolateral clavi; the venter is not preserved. These strong primaries are separated by single much weaker ribs that lack umbilical bullae and in­ ner ventrolateral tubercles. The poorly preserved inner whorls are much more finely ribbed.

Western Interior specimens referred to the species have finely and evenly ribbed inner whorls (fig. 62A, D, F, L, O); the ribs are equal, crowded, straight, and prorsiradiate on the flanks. This stage is succeeded, at variable diameters, by a growth stage in which the ribs differentiate into stronger primaries with umbilical bullae, strong inner, and weaker outer ventrolateral tubercles, separat­ ed by much weaker ribs that lack bullae and inner ventrolateral tubercles, but have feeble or effaced outer ventrolaterals; as many as four and as few as one of these weaker ribs may separate the stronger primaries. Ribbing of this type extends onto the body chamber of USNM 498339 (fig. 62P), interpreted as an adult.

The suture is moderately incised, as in P. hyatti .

DISCUSSION: Prionocyclus albinus may represent a paedomorphic derivative of Prionocyclus hyatti in which the crowded ornament and variable rib strength of juveniles of the latter are retained to maturity. Small specimens of the two species are liable to be confused, but in middle growth, the change to more distant ribbing in P. hyatti is dis­

1988: 83, 84, pl. 2, fig. 11; pl. 18, figs. 4–9; text­figs. 28, 29b, e, j.

Prionocyclus macombi Meek. Emerson et al., 1994: 212 , 378.

Prionocyclus macombi Meek, 1876 . Reyment and Kennedy, 2001: figs. 2e–h, 4.

tinctive, and the two species reach maturity at widely differing diameters.

OCCURRENCE: Prionocyclus hyatti Zone, Smith County , Kansas; Emery County, Utah ; Sandoval County, New Mexico ; Dallas County, Texas. The type material is from the Turonian of the Czech Republic .

Prionocyclus macombi Meek, 1876 Figures 63–74

Prionocyclus ? macombi Meek, 1876b: 132 , pl. 2, fig. 3a–d.

Prionocyclus ? macombi Meek. Stanton, 1894: 172 , pl. 41, figs. 1–5.

Prionocyclus ? macombi Meek. Logan, 1898: 264 .

Prionocyclus macombi Meek. Johnson, 1903: 139 .

Prionocyclus macombi Meek. Grabau and Shimer, 1910: 288 , fig. 1510e–g.

Prionocyclus macombi Meek. Diener, 1925: 155 .

Prionocyclus macombi Meek. Kauffman, 1977 : pl. 26, figs. 4, 5.

Prionocyclus macombi Meek. Hook and Cobban, 1980: 46 , text­fig. 5A–G.

Prionocyclus macombi Meek. Hill, 1982 : fig. 22H, I.

Prionocyclus macombi Meek. Cobban, 1984a: 86 .

Prionocyclus macombi Meek. Cobban, 1986 : fig. 7D, E.

Prionocyclus macombi Meek, 1876b . Kennedy,

TYPES: The lectotype here designated is USNM 20259, the original of Meek, 1876b: plate 2, figure 3 (fig. 63A, B), from the Juana Lopez Member of the Carlile Shale of Colfax County, New Mexico, middle Turonian Prionocyclus macombi Zone. Meek refers to more than one specimen of Prionocyclus ? macombi in his original account, indicating the species to be based on a type series. The lectotype is the original of his plate 2, figure 3a–c, and the original of his figure 3d may conceivably be the inner whorls of this specimen.

DIAGNOSIS: A moderate­size species that occurs as an early form with arched venter and a later form with flattened venter. Keel low and notched into as many as three or four clavi per rib. The gracile form is exceptionally compressed and has densely ribbed innermost whorls; the outer adult whorls are nearly smooth. The robust form has coarser and stronger ornament than the gracile form; ribs support nodate to bullate umbilical tubercles and nodate to spinose inner ventrolateral tubercles, whereas outer ventrolateral clavi are barely perceptible or absent.

DESCRIPTION: Robust and gracile forms of Prionocyclus macombi are distinct from the early growth stages on. During middle and later growth stages, it is also possible to recognize an early form of the species, where the venter is distinctively arched and rounded (figs. 68L, 71A–D, 72, 73) and a late form in which the venter is flattened (e.g., fig. 68P).

The earliest growth stages are highly variable and individuals may be nearly smooth (fig. 67Y, Z) to densely ribbed (fig. 67A–E) in the gracile form. The smoothest variants have distant umbilical bullae and tiny outer ventrolateral clavi, even though flank ornament is virtually absent. Densely ribbed juveniles generally have up to 16 strong primary ribs, sometimes feebly bullate, and giving rise to bundles of ribs. One to four weak­ er primary and intercalated ribs occur between the stronger ribs and extend to the umbilicus or arise on the inner flank. Ribs are prorsiradiate and straight to feebly flexuous across the flanks. They project forward and are concave over the ventrolateral shoul­ der. Weak inner ventrolateral and clavate out­ er ventrolateral tubercles are present on the stronger primary ribs; the weaker primary and intercalated ribs are feebly or nontuberculate. This densely ribbed stage terminates abruptly in most specimens by about 15–20 mm diameter or less.

Dimensions, ratios, and number of ribs per whorl of three nuclei are given in table 8. At this stage, the shell is compressed and highwhorled with a small umbilicus comprising as little as 17% of the shell diameter with whorl breadth to height ratios of as little as 0.5. The umbilical wall inclines outward and merges with a broadly rounded umbilical shoulder. The flanks are flattened and subparallel, and the ventrolateral shoulders are broadly rounded. The venter is arched in early forms, and more flattened in later ones. Delicate umbilical bullae of variable strength and generally 14–20 per whorl perch on the umbilical shoulder (fig. 67Q–X). They give rise to narrow, flexuous prorsiradiate ribs that terminate in small clavate to bullate inner ventrolateral tubercles. Outer ventrolateral tubercles may also be present, linked to the inner by prorsiradiate ribs, but disappear in early middle growth. The wide interspaces between these bullate primaries bear weak ribs that arise at the umbilical seam or low on the flanks plus lirae and growth striae (fig. 67Q–X). These weaker ribs may bear inner, but not outer ventrolateral tubercles, giving the shell a distinctive appearance when viewed ventrally (fig. 69B, C). Ornament sweeps forward and is concave over the ventrolateral shoulder, forming an acute ventral chevron. The keel is minutely and evenly serrated, the serrations far exceeding the ribs in number (figs. 69A–C, F, G; 70A–C). The largest gracile forms are still septate at 150 mm diameter (table 9). These specimens are ornamented by distant, narrow prorsiradiate ribs with weak umbilical bullae, up to 26 per whorl, separated by broad interspaces that are smooth on molds. Most specimens only have inner ventrolateral clavi at this stage, while there are some specimens with clavi intercalated between the ribs or even short intercalated ribs. Riblets and striae form an acute chevron on the venter, while the keel remains minutely serrated when well preserved.

Robust forms have a much wider umbilicus and the whorl section varies from slightly compressed to depressed. In juveniles (fig. 67F–P) there are usually approximately 12 prominent umbilical bullae per whorl. These give rise to distant, narrow, rounded, straight, prorsiradiate primary ribs separated by wide interspaces, smooth on most molds. Bullae may be equal in strength or vary, while a few specimens have shorter intercalated ribs (fig.

1876. USNM 7729D. This specimen bears the label 7729 in the same hand as the figured syntypes, and appears to be a previously unrecognized syntype, now paralectotype of the species. Middle Turonian Scaphites warreni Zone, Wall Creek Member of the Frontier Formation near Medicine Bow, Carbon County, Wyoming. Figure is X0.9. 69H, I). All ribs terminate in conical to feebly clavate inner ventrolateral tubercles, which may be equal or of variable strength. Broad ribs sweep forward to feeble outer ventrolateral clavi, which are lost early in middle growth. The ventral keel is entire and minutely serrated. If inner ventrolateral tubercles are strong, the umbilical seam and wall of the succeeding whorl may be notched to accommodate them (fig. 69H). The venter is rounded or arched in early forms (fig. 68J– L), flattened in later ones (fig. 68F–I, O, P). As size increases, ornament may coarsen markedly, and a common variant has a depressed, polygonal coastal whorl section, strong conical umbilical bullae displaced out

TABLE 10 Dimensions of Prionocyclus wyomingensis Meek, 1876 a

a little from the umbilical wall, low, broad, distant radial ribs, effaced at midflank, and blunt, conical inner ventrolateral horns. There may be low, blunt ventrolateral ribs with feeble tubercles between (figs. 72H, I). The keel commonly lacks regular serrations on the internal mold.

The largest fragments of the robust form are still septate at whorl heights of 70 mm, corresponding to an estimated diameter of 220 mm (table 9). Ornament consists of coarse, distant bituberculate ribs, the inner ventrolateral tubercles developing into sharp horns on molds, while there are occasional feeble intercalated ventrolateral tubercles. A body chamber fragment with a whorl height of 90 mm shows weakening umbilical bul­ lae and a sharpening of ribs plus strong growth striae and lirae on the umbilical wall suggesting maturity at a size of 220–250 mm diameter. The fairly simple suture (fig. 74) has been illustrated by Meek (1876b: pl. 2, fig. 3c) and by Stanton (1894: pl. 41, fig. 3).

DISCUSSION: Differences between Prionocyclus macombi and P. hyatti are discussed above. Prionocyclus bosquensis Kennedy, 1988 (86, pl. 18, figs. 1–3, 10, 11; text­fig. 29a, d, f–i; figs. 76, 77), which is known only from crushed specimens, differs from P. macombi in showing bunching of ribs at umbilical bullae as well as persistence of inner and outer ventrolateral tubercles in middle growth. P. wyomingensis (figs. 78–87) is

TABLE 11 Dimensions of Prionocyclus novimexicanus (Marcou, 1858) a

known mostly from the gracile form, which exhibits much stronger, coarser ribbing than that of P. macombi with slender whorls. In addition, in P. wyomingensis the ribs sometimes arise in groups from bullae, and an inner lateral bulge or tubercle and a fingerlike septate horn on the inner ventrolateral tubercle develop at maturity.

OCCURRENCE: Prionocyclus macombi has been found in a wide belt paralleling the western shoreline of the basal late Turonian seaway that extends from western South Dakota southwestward to central Utah and then southeastward through most of New Mexico (fig. 75). The species is also known from north­central Texas.

Prionocyclus bosquensis Kennedy, 1988 Figures 76 , 77

Prionocyclus bosquensis Kennedy, 1988: 86 , pl. 18, figs. 1–3, 10, 11; text­figs. 29a, d, f–i.

Prionocyclus bosquensis Kennedy, 1988 . Emerson et al., 1994: 212, 378.

TYPES: Holotype is OUM KT 3854 (fig. 76D); there are numerous paratypes of which the following are illustrated: OUM KT 3281 (fig. 76B), 3801b (fig. 76C), 3858 (fig. 76A), 3868 (fig. 77B), 3869 (fig. 76E), 3870 (fig. 77A), and 3873 (fig. 77C), from the top 6–7 m of the South Bosque Formation , Cement Works , 10 km (6 mi) southwest of Waco , McLennan County; also OUM KT 5375–85 , pyritic juveniles from the same locality and horizon; OUM KT 5372 a, b collected in situ 3 m below the base of the Austin Chalk at this locality; OUM KT 5373 a, b from 1 m below the Austin Chalk ; upper Turonian Scaphites whitfieldi zone .

DIAGNOSIS: A small densely ribbed species with a minutely notched keel. Ribs flexuous and not distinctly separated into primaries and secondaries.

DESCRIPTION: This species has been fully described by Kennedy (1988: 86, 87): ‘‘Most specimens are 10– 45 mm diameter, are crushed, and retain original aragonitic shell. Coiling is fairly involute, with U = 29%. Ornament is highly variable. At one extreme are very finely ornamented individuals. These have very dense, crowded, narrow, flexuous prorsiradiate ribs, every fifth to sixth strengthened, with a tiny umbilicolateral bulla, a bullate inner ventrolateral, and an obliquely placed outer ventrolateral tubercle. The intermediate ribs generally lack umbilical bullae, and have very faint or no inner and outer ventrolaterals. There is a strong, minutely serrated siphonal keel. A few specimens may even lack differentiated ribs and bear fine, even ornament, without tubercles; some individuals show groups of 3 or so ribs arising from a bulla while all specimens bear long intercalated ribs inserted on the inner flank. These specimens usually retain their outer ventrolateral tubercles. They are linked, by strengthening of tubercles and progressive decline of the weaker, feebly tuberculate ribs to much rarer individuals with distant ribs with umbilical bullae, strong inner and weak outer ventrolaterals, the interspaces with weak to obsolete flank ribs, but short intercalated ribs on the ventrolateral shoulders and venter. There are a few much larger fragments, with whorl heights of up to 53 mm. All of these show strong distant ribs with umbilical bullae, prominent inner ventrolateral spines or tubercles, weak, or no outer ventrolaterals, and groups of riblets and growth striae extending from the inner ventrolateral nodes towards the mid­venter. Between these ribs are much finer intercalated

TABLE 12 Dimensions of Prionocyclus germari (Reuss, 1845) a

riblets and lirae. There is a strong crenulate siphonal keel. Sutures not seen.’’

DISCUSSION: See Kennedy (1988: 88).

OCCURRENCE: As for types.

Prionocyclus wyomingensis Meek, 1876 Figures 78–87

Ammonites serrato­carinatus Meek, 1870: 429 .

Ammonites ( Pleuroceras ?) serrato­carinatus Meek, 1871: 298 .

Prionocyclus wyomingensis Meek, 1876a: 452 , footnote.

Prionocyclus wyomingensis Meek. White, 1880: 35 , pl. 15, fig. 1a–e.

non Prionocyclus wyomingensis Meek. Whitfield, 1880: 440 , pl. 14, figs. 1–3 (= P. novimexicanus (Marcou) .

Prionocyclus wyomingensis Meek. White, 1883: 35 , pl. 15, fig. 1a–e.

Prionocyclus wyomingensis Meek. Boyle, 1893: 243 .

Prionocyclus wyomingensis Meek. Stanton, 1894: 171 , pl. 40, figs. 1–4.

Prionocyclus wyomingensis Meek. Gilbert, 1896: 565 , pl. 58, figs. 1–3.

Prionocyclus wyomingensis Meek. Logan, 1898: 463 , pl. 106, figs. 1–4.

Prionocyclus wyomingensis Meek. Johnson, 1903: 139 .

Prionocyclus wyomingensis Meek. Barbour, 1903 : pl. 5, figs. 4, 5.

Prionocyclus wyomingensis Meek. Grabau and Shimer, 1910: 228 , fig. 1510a–d.

Prionocyclus wyomingensis Meek. Diener, 1925: 155 .

Prionocyclus reesidei Sidwell, 1932: 318 (pars), pl. 49, figs. 10, 11 only.

Prionocyclus wyomingensis Meek. Roman, 1938: 457 , pl. 46, fig. 435.

Prionocyclus wyomingensis Meek. Shimer and Shrock, 1944: 593 , pl. 247, figs. 3, 4.

Prionocyclus wyomingensis Meek. Haas, 1946 and varieties robusta (p. 200), non var. elegans (p. 210) (= P. novimexicanus ); pl. 18, figs. 3– 6; non pl. 19, figs. 1–7, 11–14 (= P. novimexicanus ); pl. 20, figs. 1–3, 5–7, non pl. 20, fig. 4 (= P. novimexicanus ); pl. 22, figs. 3–5; non pl. 22, figs. 1, 2 (= P. novimexicanus ); pl. 23, figs. 1, 3 (in part); pl. 24, figs. 2, 3; text­figs. 93–97, 105–108; non 98–104 (= P. novimexicanus ).

TABLE 13 Dimensions of Prionocyclites mite Kennedy, 1988 a

Prionocyclus wyomingensis Meek. Wright, 1957: 426 , fig. 547. 6a, 6b.

Prionocyclus wyomingensis Meek. Termier and Termier, 1960 : fig. 2418.

Prionocyclus wyomingensis Meek. Matsumoto, 1965: 18 , pl. 16, fig. 1a–c; pl. 17, fig. 2a–c; pl. 18, fig. 1a–c (? = P. novimexicanus ).

Prionocyclus wyomingensis Meek. Matsumoto, 1971: 132 , pl. 21, fig. 2; pl. 22, fig. 1, text­fig. 2.

Prionocyclus wyomingensis Meek. Hattin, 1975b : pl. 2, fig. 11.

Prionocyclus wyomingensis Meek. Kauffman, 1977 : pl. 26, figs. 2, 3.

Prionocyclus wyomingensis Meek, 1876 . Kennedy et al., 1989: 91, fig. 24E.

Prionocyclus wyomingensis Meek, 1876 . Kennedy, 1988: 88, pl. 14, fig. 8.

Prionocyclus wyomingensis Meek, 1876 . Hall et al., 1994: 305, figs. 4I, N, O, 5A–C, G–J.

Prionocyclus wyomingensis Meek. Emerson et al., 1994: 212 , 378.

Prionocyclus wyomingensis Meek. Wright, 1996: 186 , fig. 4a, b.

Prionocyclus wyomingensis Meek, 1876 . Reyment and Kennedy, 2001: fig. 3.

TYPES: Lectotype, by the subsequent designation of Matsumoto, 1965: 18 is USNM 7729 , the original of Stanton, 1894: plate 40, figure 3 (fig. 78); two paralectotypes have the same number and are the originals of Stanton, 1894: plate 40, figures 1, 2 (figs. 79, 80). A further probable unfigured paralectotype bears the number 7729D, and is shown in figures 82, 83. All are from what is now known as the Wall Creek Sandstone Member of the Frontier Formation in the Medicine Bow River valley of Southeast Wyoming (fide Cobban, 1984a: 86).

DIAGNOSIS: A large species for the genus; moderately evolute; keel notched into more siphonal clavi than ribs. Gracile form has closely spaced prorsiradiate primary and secondary ribs. Primary ribs bear lengthy umbilical bullae that may divide into shorter umbilical bullae and bullate or nodate inner lateral tubercles. All primaries bear nodate inner ventrolateral tubercles and weaker cla­ vate to bullate outer ventrolateral tubercles. Robust form has coarse ribs that support prominent nodate umbilical tubercles, nodate inner ventrolateral tubercles, and weak outer ventrolateral clavi.

DESCRIPTION: The robust form is rare (figs. 84A–F, 85D, E, H, I). Coiling is evolute with U/D = 0.30–0.37 in the available material (table 10); the umbilicus broad, the umbilical wall flattened and inclined outward, with grooves to accommodate the inner ventrolateral spines of the preceding whorl (fig. 85E). The umbilical shoulder is narrowly rounded, the whorl section slightly compressed to slightly depressed, with the greatest breadth at the umbilical bullae costally and just outside the umbilical shoulder intercostally.

Ornament is highly variable. At one extreme are very coarsely ribbed individuals with only 16 or 17 ribs per whorl. Ribs arise at the umbilical seam and strengthen into massive conical umbilical bullae, broaden and are straight and prorsiradiate across the flanks, and develop massive septate inner ventrolateral spines that generally appear as large clavi on the mold when the spines have broken off. The rib profile is somewhat concave between bulla and spine (fig. 85H, I). Broad ribs sweep forward across the ventrolateral shoulder to outer ventrolateral clavi and a smooth zone separates them from the strong and minutely serrated siphonal keel.

At the other extreme (fig. 85D, E) are similarly proportioned individuals that have 17 sharp to spinose umbilical tubercles in middle growth, each of which gives rise to a strong concave to straight and rectiradiate adapical primary rib and a much weaker adapertural primary rib, which loop to a strong inner ventrolateral clavus/spine, the arrangement resembling a bow. Broad ribs sweep forward over the ventrolateral shoulder and connect to weaker outer ventrolateral clavi. Between the looped, bullate ribs are one or two nonbullate ribs that extend to the umbilical seam or arise on the inner flanks and

2. Reduced ×0.53. Original is 386 mm in diameter.

×0.53. Original is 386 mm in diameter.

develop much weaker ventrolateral tubercles, the arrangement giving the shell a highly irregular ornament. The largest robust individual seen is 83 mm in diameter.

Gracile individuals are common (figs. 78– 81;?82,?83; 84G–J, 85A–C, F, G). At 40 mm diameter, coiling is evolute, with U/D = 0.26 (table 10); the umbilicus is shallow, with a low flattened umbilical wall. The whorls are high and compressed (whorl breadth to height ratio averages 0.79), with fine, dense, crowded ribs. There are up to 12 weak umbilical bullae that give rise to single or paired ribs, with single nonbullate ribs between that extend to the umbilicus or not, yielding a total of 44–48 ribs per whorl. Ribs are crowded, flexuous, and prorsiradiate, with small bullate to clavate inner, and clavate outer ventrolateral tubercles.

In middle growth, specimens have up to 70 ribs per whorl. There are up to 18 bullae per whorl, initially at the umbilical shoulder, but tending to move out to the inner flanks, when a new bulla develops (fig. 81C). They are the bases of septate umbilical spines, and give rise to pairs of coarse ribs that are straight and prorsiradiate and initially loop to outer ventrolateral tubercles that are also the bases of septate spines. As size increases, the tendency to loop declines and the adapertural rib of the pair may detatch. There are one to six weaker, nonbullate long ribs between the bullate ones, each of which may develop a weak inner ventrolateral tubercle.

The ribs sweep forward over the ventrolateral shoulder to small, obliquely placed outer ventrolateral tubercles and form an acute chevron with the high and minutely serrated siphonal keel. The largest gracile individuals are 220–230 mm diameter. At maturity, the bullate ribs strengthen markedly and are very coarse, high, and barlike. Where well­preserved, they bear long inner lateral and inner ventrolateral spines, while sharp outer ventrolateral clavi are also present. Between are up to three much weaker, narrow, sharp long ribs that lack any trace of a tu­

cou, 1858). USNM 498423, see also Figure 96 . Reduced ×0.53. The original is 380 mm in diameter.

bercle. This coarseness and marked differentiation of the main ribs gives a highly characteristic appearance to the shell.

The largest collection studied consists of 73 specimens from the Frontier Formation at USGS Mesozoic locality D 9244 in southeastern Wyoming. Of these specimens 61 are the gracile form and 12 are the robust form.

The suture is fairly simple and typical of the genus. The suture from White (1880) is shown here (fig. 87).

DISCUSSION: Differences between P. wyomingensis , P. macombi , and P. bosquensis are noted above. P. wyomingensis most closely resembles P. novimexicanus (Marcou, 1858) (figs. 88–101), which is presumably its descendant, but the latter is even more compressed, has flexuous ribs, seldom develops the umbilical and inner lateral tuberculation of P. wyomingensis and loses the outer ventrolateral tubercles at a very early stage so that the primary ribs are effectively bituberculate.

A remarkable pathological specimen (collected by J. I. Kirkland, Salt Lake City, Utah), USNM 475903 (fig. 86), from the Juana Lopez member of the Mancos Shale in the SE ¼ sec. 4, T. 12 S, R. 1 E, Garfield County, Colorado, lacks a siphonal keel (fig. 86).

OCCURRENCE: Prionocyclus wyomingensis is widely distributed in the Western Interior of the United States from northwestern Montana south through much of New Mexico, and from east­central Utah to southwestern Kansas. It has also been figured recently from Alberta, Canada (Hall et al., 1994) and is known from Japan (Matsumoto, 1971).

Prionocyclus novimexicanus (Marcou,

1858)

Figures 88–101

Ammonites novi­mexicani Marcou, 1858: 35 , pl. 1, fig. 2. Prionocyclus wyomingensis Meek. Whitfield, 1880: 440 , pl. 14, figs. 1–3. Prionocyclus wyomingensis Meek var. elegans

Haas, 1946: 200, pl. 19, figs. 1–7, 11–14; pl. 20, fig. 4; pl. 21, figs. 1–3, 5; pl. 22, figs. 1, 2; text­figs. 98–104.

Prionocyclus wyomingensis Meek. Luppov and Druschchits, 1958: 123 , text­fig. 97b, pl. 60, fig. 3.

Prionocyclus (Prionocyclus) wyomingensis var. elegans Haas. Jeletzky, 1970 : pl. 26, fig. 8.

Prionocyclus wyomingensis Meek. Kennedy and Cobban, 1976 : pl. 11, fig. 4.

Prionocyclus wyomingensis elegans Haas. Kauffman, 1977: 260 , pl. 22, fig. 14.

Prionocyclus novimexicanus (Marcou) . Hook and Cobban, 1979: 38, fig. 3E–L.

Prionocyclus novimexicanus (Marcou) . Merewether et al., 1979: pl. 3, fig. 3.

Prionocyclus wyomingensis Meek. Case, 1982 : fig. 12. 63.

Prionocyclus novimexicanus (Marcou) . Cobban, 1984b: 14, pl. 1, figs. 15, 16.

Prionocyclus novimexicanus (Marcou, 1853) . Kennedy, 1988: 83.

Prionocyclus novimexicanus (Marcou, 1848) . Kennedy et al., 1989: 93.

Prionocyclus novimexicanus (Marcou) . Cobban and Hook, 1989: fig. 10j–l.

Prionocyclus novimexicanus (Marcou, 1858) . Amédro, 1990: 269, pl. 17, fig. 6; pl. 25, figs. 1–3.

Prionocyclus novimexicanus (Marcou) . Emerson et al., 1994: 212, 378.

Prionocyclus novimexicanus (Marcou, 1858) . Reyment and Kennedy, 2001: fig 2i–m.

TYPES: The lectotype, here designated, of Ammonites novimexicani Marcou, 1858 , is BMNH C49764 (fig. 88A–C), either from near Albuquerque, New Mexico, or La Lunes, New Mexico. Marcou specifically mentions two specimens in his account, and lectotype designation is necessary. The holotype of Prionocyclus wyomingensis elegans Haas, 1946 (a synonym), is the original of Whitefield, 1880: plate 14, figure 2, from Beaver Creek, near Camp Jenney, South Dakota, USNM 12283 (fig. 89A, B).

DIAGNOSIS: This large, moderately evolute species has a keel notched into small siphonal tubercles more numerous than the ribs. The gracile form has dense, flexuous primary and secondary ribs. Primary ribs arise from elongated umbilical bullae, each of which is rarely divided into a shorter umbilical bulla and a small, nodate inner lateral tubercle. All primaries bear rounded to clavate inner ventrolateral tubercles. Outer ventrolateral tubercles are usually absent, and very weak if present. The robust form is more evolute and more sparsely ribbed. Looped ribs may connect umbilical and inner ventrolateral tubercles in both gracile and robust forms.

DESCRIPTION: The best example of the robust form is USNM 498417 (fig. 99F, G). Coiling is very evolute, with U/D = 0.48, the umbilical wall flattened and inclined outward, the umbilical shoulder broadly round­ ed, the flanks convergent with the greatest breadth at the umbilical shoulder intercostally and at the umbilical bulla in costal section. The whorl section is compressed, with a costal whorl breadth to height ratio of 0.73 up to a shell diameter of 60 mm (table 11). Ornament consists of blunt umbilical bullae, 18 per whorl. These give rise to broad, low, straight prorsiradiate ribs that weaken markedly at midflank, and connect to blunt inner ventrolateral bullae. Broad ribs sweep forward and decline, forming an acute chevron with the minutely serrated siphonal keel; there is no trace of an outer ventrolateral tubercle. Beyond 60 mm, the bullae weaken progressively, and commonly give rise to pairs of ribs, which may loop to the inner ventrolateral bullae (fig. 100C, D) or not. Between are one or two weaker nonbullate ribs, arising at the umbilical shoulder or low on the flanks with feeble inner ventrolateral tubercles or not. The ribs become feebly flexuous at this stage.

The gracile form is represented by numerous specimens (figs. 88–95, 98A–C). Coiling is moderately evolute, with a shallow umbilicus with U/D = 0.26–0.30 between 50 and 100 mm shell diameter; the umbilicus is shallow, with a flattened wall. The whorl section is compressed, with whorl breadth to height ratios of 0.5–0.7 (table 11), the greatest breadth at the umbilical bullae in costal section and just outside the umbilical shoulder intercostally.

The earliest growth stages seen are characterized by very fine, dense, crowded ornament. Feeble umbilical bullae give rise to pairs or groups of three ribs; between are up to nine ribs which arise at the umbilical shoulder, low, or high on the flanks. The degree of differentiation between strong and bullate and weak and nonbullate ribs varies greatly between individuals (figs. 90–92), with up to 90 ribs per whorl. In middle growth, to a diameter of 70–80 mm, ribbing varies greatly in strength and density between individuals (compare fig. 90L and fig. 99A, B). Typically, there are 14–18 bullae per whorl that give rise to pairs or groups of ribs, with nonbullate intercalaries between, the bullate ribs looping in pairs to inner ventrolateral clavi, the nonbullate ribs with feeble inner ventrolateral tubercles or not. Feeble outer ventrolateral tubercles are present only at diameters of less than 15–20 mm. Beyond, ribs sweep forward over the ventrolateral shoulder to form an acute chevron. The siphonal keel is high, strong, and minutely serrated.

An adult of the gracile form has a maximum diameter of 386 mm (figs. 94, 95). It retains the crowded ornament of ribs of varying strengths to a diameter of 170 mm, beyond which the minor ribs decline progressively so that by the middle section of the body chamber, ornament consists of very distant, coarse, convex prorsiradiate ribs with strong, subspinose umbilical bullae and enormous, slender septate inner ventrolateral horns that persist to the last section of the body chamber. Just before the adult aperture, ribbing stops and the last section is covered in dense irregular riblets, lirae, and striae.

USNM 498423 (figs. 96, 97) is an uncrushed body chamber mold. The whorl height is 98 mm at the end of the phragmocone, and the diameter of the specimen is 380 mm, which suggests a total diameter of over 400 mm. The whorl section at the end of the phragmocone is trapezoidal with a whorl breadth to height ratio of 0.95. Ornament consists of strong, distant, coarse primary ribs, with umbilical bullae that decline in strength as size increases. There are massive conical inner ventrolateral tubercles at the end of the phragmocone and beginning of the body chamber. They weaken on the later part of the body chamber. Narrow ribs project forward over the venter to form a chevron, with finer and irregular riblets between. The siphonal keel is blunt on the mold, and irregularly notched.

The suture has a broad, bifid E/L, narrow L, and bifid L/U 2 (fig. 101).

DISCUSSION: Prionocyclus novimexicanus most closely resembles its presumed ancestor, P. wyomingensis (figs. 78–87); differences are discussed above. Prionocyclus quadratus (figs. 102–107) and P. germari (figs. 109–119) never show the marked differentiation of rib strength of juvenile P. novimexicanus ; instead the ribbing is even. The whorls are never as depressed or as finely ribbed, although P. quadratus and P. germari lose their outer ventrolateral clavi at very small diameters, as does P. novimexicanus . Prionocyclus quadratus develops a pronounced outer lateral bulge when adult (figs. 116–118), while the umbilical bullae commonly migrate out to an inner flank position in middle and late growth.

OCCURRENCE: Widely distributed in the Western Interior in the upper Turonian Zone of Scaphites whitfieldi . Specimens have been found in south­central and southeastern Montana, central and eastern Wyoming, western South Dakota, eastern Utah, and over much of Colorado and New Mexico. It has also been recorded from Trans­Pecos Texas (Kennedy et al., 1989), and Tunisia (Amédro, 1990).

Prionocyclus quadratus Cobban, 1953 Figures 102–107

Prionocyclus reesidei Sidwell, 1932: 354 (pars.), pl. 49, fig. 12 only.

Prionocyclus quadratus Cobban, 1953: 354 , pl. 48, figs. 1–8.

Prionocyclus reesidei Sidwell. Kauffman, 1977: 260 , pl. 2, figs. 2, 3.

Prionocyclus quadratus Cobban. Kauffman, 1977: 256 , pl. 19, figs. 11, 12; pl. 26, fig. 1.

non Prionocyclus quadratus Cobban. Merewether et al., 1979 : pl. 3, figs. 6–8 (= P. germari ).

Prionocyclus quadratus Cobban, 1953 . Kennedy, 1988: 83.

Prionocyclus quadratus Cobban. Cobban and Hook, 1989 , fig. 10H, I.

TYPES: Holotype is USNM 108332 (fig. 103), paratypes USNM 108333a–c (figs. 104–106), from the upper Turonian Sage Breaks Member of the Carlile Shale in sec. 33, T. 9 S, R. 61 E, Carter County, Montana. Paratype USNM 108334 (fig. 102) is from a septarian concretion bed 12.8 m above the base of the Sage Breaks Member 14.5 km south­southeast of Rapid City in the NE ¼ sec. 22, T. 1 S, R. 8 W, Pennington County, South Dakota. Paratype USNM 108335 is from a septarian concretion bed 5.2 m below the top of the Turner Sandy Member of the Carlile Shale 10.4 km north of Belle Fourche, in the E ½ sec. 2, T. 9 N, R. 2 E, Butte County, South Dakota.

DIAGNOSIS: A fairly large species that has sparsely ribbed adult whorls with strong primary ribs and weak secondary ribs. Primary ribs on the robust form have umbilical bullae, nodate inner ventrolateral tubercles, and midflank swellings or weak tubercles. The gracile form usually lacks midflank swellings. No clearly defined outer ventrolateral tubercles occur on either form.

DESCRIPTION: The types represent the robust form of the species. The holotype, USNM 108332 (fig. 103), is part of a small adult body chamber that has an intercostal width of 32.5 mm and height of 34.3 mm (ratio = 0.95) and a costal width of 42.0 mm and height of 38.2 mm (ratio = 1.10), with the greatest width at the umbilical shoulder. The specimen is an internal mold that does not have serrations on the keel preserved. A smooth ventral groove bounds the keel. Rib­ bing consists of strong, narrow, prorsiradiate primaries alternating with very weak, narrow secondaries. All ribs are straight on crossing the flanks, but they bend sharply forward on the ventrolateral shoulder and fade out on the venter. Primary ribs support umbilical bullae, weak midflank bullae, and blunt ventrolateral tubercles. Secondary ribs arise low on the flanks and efface on the venter without developing into ventrolateral tubercles.

A paratype, USNM 108334 (fig. 102), about 43 mm in diameter, has 42 ribs per whorl at a diameter of 30 mm with two or three secondaries separating primaries. At a larger diameter, most primaries are separated by a single secondary.

The suture figured by Cobban (1953: pl. 48, fig. 4) has a rather long lateral lobe, and a similar feature is shown in figure 107.

DISCUSSION: The species attains a large size, with some phragmocones having diameters of as much as 250 mm. Large specimens occasionally have blunt, nodate mid­ flank tubercles. Keels are notched with more serrations than ribs.

The bulk of the specimens at hand represent the robust form. The gracile form tends to be more densely ribbed and lacks midflank swellings or bullae. Outer ventrolateral tubercles seem to be absent on both robust and gracile forms.

OCCURRENCE: Upper Turonian Scaphites nigricollensis and S. corvensis zones of the northern Great Plains of south­central and southeastern Montana and western South Dakota, and in equivalent strata in west­central New Mexico.

Prionocyclus germari (Reuss, 1845) Figures 108A, B, D–F; 109–119

Ammonites Germari Reuss, 1845: 22 , pl. 7, fig. 10.

Ammonites Germari Reuss. Schlüter, 1872: 41 , pl. 11, figs. 15–17.

Ammonites Germari Reuss. Fritsch, 1872: 29 , pl. 14, figs. 1, 2; pl. 16, fig. 7.

Ammonites Schlönbachi Fritsch, 1872: 33 , pl. 16, fig. 5.

Schlönbachia Germari Reuss. Fritsch, 1893: 74 , fig. 50.

Germariceras germari (Reuss) . Breistroffer, 1947: unpaginated.

Germariceras germari (Reuss) . Wright, 1957: L427, fig. 547.2.

Prionocyclus carvaholi Howarth, 1966: 224 , pl. 1, figs. 8–11; pl. 2, figs. 3–6.

Prionocyclus quadratus Cobban. Scott et al., 1986 : fig. 6K.

Prionocyclus germari (Reuss) . Kaplan, 1988: 14, pl. 3, figs. 1–3, pl. 6, fig. 1.

Prionocyclus ? germari Reuss. Hall et al., 1994: 307 , fig. 4J–L.

Germariceras germari (Reuss, 1845) . Wright, 1996: 186, fig. 142. 1a–c.

Prionocyclus germari (Reuss) . Wiese, 1997: fig. 7.4.

Prionocyclus germari (Reuss, 1845) . Kaczsrowski, 2000: 244, fig. 3a.

Prionocyclus germari (Reuss, 1845) . Reyment and Kennedy, 2001: fig. 2.

TYPE: The lectotype, here designated, is the original of Reuss, 1845: 22, plate 7, figure 10, from the ‘‘Planermergel von Werschowitz.’’ The original figure is reproduced here as figure 109K.

DIAGNOSIS: Moderately to rather widely spaced, generally rounded, prorsiradiate ribs on the outer whorls characterize this species. Primary and secondary ribs tend to be of nearly uniform height. The keel is finely notched with many more serrations than ribs. The robust form has ribs that support bullate to nodate umbilical tubercles and nodate to clavate inner ventrolateral tubercles; weak outer ventrolateral clavi are present on some juveniles. The gracile form is weakly ribbed.

DESCRIPTION: Robust and gracile forms can be recognized starting from very small diameters. In the juvenile robust form (fig. 113A–P, T, U), the coiling is fairly evolute, with the umbilical wall notched to accommodate the inner ventrolateral nodes of the preceding whorl; the umbilicus represents 36–38% of the diameter (table 12) with a flattened wall and broadly rounded umbilical shoulder. The intercostal whorl section is slightly compressed with the greatest breadth just outside the umbilical shoulder; the costal section is polygonal with the greatest breadth at the umbilical bullae. There are 16–24 ribs per whorl between 25 and 60 mm in most specimens. The ribs arise at the umbilical seam and bear well­developed umbilical bullae that migrate out to an inner flank position at as little as 20 mm diameter. These give rise to broad, blunt, crowded prorsiradiate ribs that are usually evenly developed, with only occasional irregularities. All bear feebly clavate to conical flat­topped inner ventrolateral tubercles that are the bases of long septate spines housed in grooves in the umbilical wall of the succeeding whorl, but rarely preserved (fig. 113X, Y). Low, broad, weakening ribs sweep forward and form an acute chevron with the line of the siphonal keel. Feeble outer ventrolateral clavi are present up to 15 mm diameter, but are thereafter lost, and the ribs are bituberculate. The strong siphonal keel is minutely and evenly crenulat­ ed. Larger specimens (figs. 113Q–S, V–Y, 114–118) vary in strength and coarseness of ribbing, with as few as 22 ribs of equal or unequal strength at 90 mm diameter, at which size the umbilical bullae migrate well out to the inner flank. This coarse, even or uneven ornament extends to the largest diameters seen.

The gracile form (figs. 109–112) has a whorl breadth to height ratio of 0.66–0.90 between 25 and 60 mm diameter (table 12). The coiling is evolute, with U = 35–40% of diameter; the umbilicus is shallow, with a low wall. Very crowded, even, primary ribs arise at the umbilical seam and strengthen across the flanks with no or only incipient bullae. Ribs are straight to feebly flexuous, and prorsiradiate on the flanks, where occasional long intercalated ribs yield a total of up to 70 ribs per whorl. Each rib bears a tiny conical to feebly clavate inner ventrolateral tubercle from which a weakening rib projects forward to form an acute ventral chevron with the minutely and evenly serrated siphonal ridge. Tiny outer ventrolateral clavi are present up to a diameter of approximately 10 mm, but are thereafter lost. From 60–150 mm this even style of ribbing continues, with around 36–40 ribs per whorl, which have feeble but variably developed umbilical bullae and inner ventrolateral clavi.

The suture is fairly simple, with a moderately deep lateral lobe (fig. 119).

DISCUSSION: Absence of an outer ventrolateral tubercle distinguishes this species from Prionocyclus wyomingensis when young, while the absence of an umbilical plus inner lateral tubercle separates it from P. wyomingensis when adult. The very even and sparser ribbing of P. germani alone serves to distinguish both juveniles and adults from P. novimexicanus . Prionocyclus quadratus generally has stouter quadrate whorls, and an incipient lateral tubercle when adult.

Ammonites schlönbachi Fritsch, 1872 (33, pl. 16, fig. 5) appears to be based on a poorly preserved crushed external mold of P. germari . A plaster cast taken from the mold, apparently the basis of the original figure, is shown as figure 108A. The flank ribs and long ventrolateral spines compare well with the Western Interior example shown in figure 113X, Y. Fritsch figured an undoubted juvenile P. germari from the same horizon and locality (1872: pl. 16, fig. 7).

Prionocyclus carvaholi Howarth, 1966 (p. 224, pl. 1, figs. 8–11; pl. 2, figs. 3–6; fig. 108D–F), from the Moçâmedes Desert, Angola, appears to be based on robust variants of the present species, even though Howarth (1966: 224) described very small ‘‘upper or inner ventrolateral tubercles... represented merely by a raised portion of the rib obliquely in front of the ventrolateral spine.’’

OCCURRENCE: Fairly abundant at the top of the Frontier Formation in central Wyoming (Cobban, 1990), and in the D­Cross Tongue of the Mancos Shale in south­central New Mexico. The species is also present in the basal part of the Austin Chalk in the Rio Grande area of southwestern Texas, where it was reported as P. reesidei (Freeman, 1961) . In all of these areas, P. germari is associated with Mytiloides incertus (Jimbo) and Eubostrychoceras matsumotoi Cobban of late Turonian, Scaphites corvensis / P. germari Zone age. The species also occurs in the upper Turonian of Germany, the Czech Republic, and Angola.

Prionocyclus pluricostatus , new species Figure 120

DERIVATION OF NAME: Plurimus (Latin): most; costatus (Latin): ribbed.

TYPES: Holotype is USNM 498491 a (fig. 120D); paratypes USNM 498491 b (fig. 120D), 498492 (fig. 120A), 498493 (fig. 120B), and 498494 (fig. 120C), all from USGS Mesozoic locality D11898, calcareous shale 4 m below the base of the Fort Hays Limestone Member of the Mancos Shale , upper Turonian , upper part of Prionocyclus germari Zone, NW ¼, SE ¼, sec. 22, T. 8 S, R. 87 W, Pitkin County, Colorado.

DIAGNOSIS: A densely and evenly ribbed Prionocyclus . There are up to 80 ribs per whorl in juveniles at 20 mm diameter, with inner ventrolateral clavi and outer ventrolateral clavi, if present, lost at a very early stage. Ribs may be single or arise in pairs or groups at the umbilical shoulder, or intercalate low on the flanks. Larger specimens with up to 90 ribs per whorl at 50 mm diameter, arranged as on nuclei, but bullate ribs bear strong inner ventrolateral clavi that are sometimes linked with weaker clavi or other ribs.

DISCUSSION: The types are crushed in shale, and there is little to add to the diagnosis. Prionocyclus pluricostatus n. sp. bears a superficial resemblance to P. bosquensis (fig. 76), also known only from crushed specimens in shales. They differ in that P. bosquensis has ribs of variable strength on nuclei, and persistent inner and outer ventrolateral tubercles. This last character separates the species from P. wyomingensis (see fig. 85A–C, F, G), whereas the eveness of ribbing separates it from P. macombi (fig. 67) and P. novimexicanus (fig. 88). P. germari (figs. 109, 113) has even ribbing, but specimens are never as densely ribbed as the present form. A specimen from New Mexico figured by Johnson (1903: 139, pl. 1, fig. 15) as Prionocyclus appears to be as densely ribbed as our species, but the New Mexico species is more involute.

The types occur with Mytiloides incertus at a very high level in the Turonian. We at­ tribute them to the upper Turonian ammonite zone of P. germari , but they may represent a separate, as yet uncharacterized uppermost Turonian ammonite zone.

OCCURRENCE: As for types.

Genus Prionocyclites Kennedy, 1988

TYPE SPECIES: Prionocyclites mite Kennedy, 1988: 89 , pl. 10, figs. 7–11; text­fig. 30.

DIAGNOSIS: ‘‘Inner whorls with distant bullate primary ribs separated by groups of weaker non­bullate primaries and occasional shorter intercalated ribs, all with a ventrolateral clavus. Keel broadly undulose, not serrated. Body chamber smooth but for distant bullate primaries and associated constrictions. Aperture constricted. Suture simple, with little­incised elements’’ (Kennedy, 1988: 89).

DISCUSSION: Prionocyclites is a progenetic dwarf, presumably derived from Prionocyclus , the inner whorls of the two sharing many common features (compare fig. 121 and fig. 51A–I), although the adult body chamber and simple adult suture of Prionocyclites are quite distinctive. It most closely resembles Lymaniceras Matsumoto, 1965 , here interpreted as another progenetic dwarf collignoniceratid. However, Lymaniceras has a minutely serrated keel and lacks the Prionocyclus ­like inner whorls and paucicostate, constricted body chamber of Prionocyclites (modified after Kennedy, 1988: 89).

OCCURRENCE: Prionocyclus hyatti Zone of north­east Texas only.

Prionocyclites mite Kennedy, 1988 Figures 121 , 122

Prionocyclites mite Kennedy, 1988: 89 , pl. 10,

figs. 7–11, text­fig. 30.

Prionocyclites mite Kennedy. Emerson et al.,

1994: 211, unnumbered figure on p. 213.

TYPE: Holotype by monotypy in USNM

Figures are ×1.

420144 (figs. 121, 122; Table 13) from the Arcadia Park Formation, Eagle Ford Group at USGS locality 22608 (ex Renfro Collection), east of power plant on Mountain Creek Lake, Dallas County, Texas; Prionocyclus hyatti zone.

DIAGNOSIS: Small species characterized by its arched venter and prominent keel. Ribs are sparse, conspicuously prorsiradiate, and bear oblique ventrolateral clavi.

DESCRIPTION: ‘‘ Holotype and only known specimen is a complete adult retaining traces of original shell. Coiling moderately evolute, with shallow umbilicus, umbilical wall low, rounded. Whorl section compressed with whorl breadth to height ratio 0.66. Flanks flattened, subparallel, with broadly round ventrolateral shoulders, venter with strong, blunt, undulose siphonal keel. On phragmocone there are twelve bullate ribs per whorl separated by two slightly weaker nonbullate ribs, giving a total of thirty­three to thirtyfour ribs per whorl at the umbilical shoulder. Ribs are narrow, rounded, prorsiradiate, and straight on the inner flank, flexing forward and concave over the outer flank and ventrolateral shoulder. A few short ribs intercalate on the outer flank and all ribs bear a blunt, obliquely placed ventrolateral clavus. The ribs project forward from the clavus towards the mid­line of the venter but decline before reaching the keel. The low undulations on the keel do not correspond to the ribs; they are far fewer in number. This ornament extends on to the first part of the body chamber but thereafter rapidly declines. The last part of the body chamber is near­smooth between three very distant ribs that arise from prominent umbilical bullae. These ribs are narrow, rounded, and efface by the ventrolateral

Figures are ×1.

Figure is ×1.

shoulder. They are followed by a shallow constriction, most obvious at the ventrolateral shoulder. A much stronger constriction marks the adult aperture. Suture very simple with broad, little­incised E/L and narrower L; not approximated at the end of the phragmocone’’ (Kennedy, 1988: 89).

DISCUSSION: The only ammonites with which Prionocyclites mite Kennedy, 1988 , is likely to be confused are species of Lyman­

Figure is ×1.

iceras Matsumoto, 1965. The type species, L. planulatum Matsumoto, 1965 (31, pl. 6, figs. 1, 2; pl. 7, figs. 1–5; pl. 8, figs. 1–8; text­figs. 10–16), is also a progenetic dwarf, but without the distinctive differentiation of primary ribs seen in Prionocyclites and with a finely serrated keel. Body chambers are very different.

OCCURRENCE: As for type.

Figures

Fig. 50. Prionocyclus hyatti (Stanton, 1894). A, B. Paralectotype USNM 22941a. C–E. lectotype, USNM 22941. F–H. Paralectotype USNM 22941b. All specimens are from the Middle Turonian P. hyatti Zone, Codell Sandstone (Pugnellus Sandstone) of Williams Creek and Poison Canyon, Huerfano Park, Colorado. All figures are X1.

Fig. 62. Prionocyclus albinus (Fritsch, 1872). A. USNM 498333, from locality 32. B. USNM 220385, from locality 22. C–E. USNM 498334, from USGS Mesozoic locality 35. F. USNM 498335, from locality 63. G, H. USNM 498336, from locality 32. I–K. USNM 356899, from locality 40. L, M. USNM 498337, from locality 63. N, O. USNM 498338, from locality 32. P. USNM 498339, from locality 32. All figures are X1.

Fig. 63. Prionocyclus macombi Meek, 1876. A, B. lectotype, USNM 20259, from the Juana Lopez Member of the Carlile Shale in Colfax County, New Mexico. C–G. USNM 22940, the originals of Stanton, 1894, plate 41, figures 1–3, from ‘‘near Mancos, southwestern Colorado, about 400 feet above the base of the Colorado Cretaceous shales, where it is associated with Ostrea lugubris and Inoceramus dimidius.’’ Figures A–C, E–G are X1; figure D is X2.

Fig. 64. Prionocyclus macombi Meek, 1876. A, B. USNM 498353; C. USNM 498354; D–F. USNM 498355; G. USNM 498356; H. USNM 498357; I. USNM 498358; J–L. USNM 498359; M–O. USNM 498360, all variants of the gracile form, from locality 27. All figures are X1.

Fig. 76. Prionocyclus bosquensis Kennedy, 1988. A. Paratype OUM KT 3858. B. Paratype OUM KT 3281. C. Paratype OUM KT 3801b. D. Holotype, OUM KT 3854. E. Paratype OUM KT 3869. All specimens are from the upper Turonian Scaphites whitfieldi Zone, South Bosque Formation, 10 km (6 mi) southwest of Waco, McLennan County, Texas. All figures are X2.

Fig. 77. Prionocyclus bosquensis Kennedy, 1988. A. Paratype OUM KT 3870. B. Paratype OUM KT 3868. C. Paratype OUM KT 3873. All specimens are from the lower upper Turonian Scaphites whitfieldi Zone, South Bosque Formation, 10 km (6 mi) southwest of Waco, McLennan County, Texas. All figures are X1.

Fig. 78. Prionocyclus wyomingensis Meek, 1876. Lectotype, USNM 7729, middle Turonian Scaphites warreni Zone, Wall Creek Member of the Frontier Formation near Medicine Bow, Carbon County, Wyoming. Figures are X1.

Fig. 79. Prionocyclus wyomingensis Meek, 1876. Paralectotype, USNM 7729, middle Turonian Scaphites warreni Zone, Wall Creek Member of the Frontier Formation near Medicine Bow, Carbon County, Wyoming. Figures are X1.

Fig. 80. Prionocyclus wyomingensis Meek, 1876. Paralectotype, USNM 7729, middle Turonian Scaphites warreni Zone, Wall Creek Member of the Frontier Formation near Medicine Bow, Carbon County, Wyoming. Figures are X1.

Fig. 96. Prionocyclus novimexicanus (Marcou, 1858). USNM 498423, robust form from locality 4. Reduced ×0.53. The original is 380 mm in diameter.

Fig. 102. Prionocyclus quadratus Cobban, 1953. Paratype USNM 108334, Sage Breaks Member of the Carlile Shale, 14.9 km (9 mi) south­southeast of Rapid City, in the NE¼ sec. 22, T. 1S, R. 8W, Pennington County, South Dakota. Figure is ×1.

Fig. 103. Prionocyclus quadratus Cobban, 1953. Holotype, USNM 108332, Sage Breaks Member of the Carlile Shale, sec. 63, T 9S, R 61E, Carter County, Montana. Figures are ×1.

Fig. 104. Prionocyclus quadratus Cobban, 1953. Paratype, USNM 108333c, Sage Breaks Member of the Carlile Shale, sec. 63, T 9S, R 61E, Carter County, Montana. Figures are ×1.

Fig. 105. Prionocyclus quadratus Cobban, 1953. Paratype, USNM 108333b, Sage Breaks Member of the Carlile Shale, sec. 63, T 9S, R 61E, Carter County, Montana. Figures are ×1.

Fig. 106. Prionocyclus quadratus Cobban, 1953. Paratype, USNM 108333a, Sage Breaks Member of the Carlile Shale, sec. 63, T. 9S, R. 61E, Carter County, Montana. Figures are ×1.

Fig. 107. Partial external suture of Prionocyclus quadratus Cobban, 1953. USNM 498451, from the Sage Breaks Member of the Carlile Shale in the SW¼ sec. 32, T. 50N, R. 66W, Crook County, Wyoming.

Fig. 120. Prionocyclus pluricostatus n. sp. A. Paratype USNM 498492; B. Paratype USNM 498493; C. Paratype USNM 498494; D. Holotype USNM 498491a (left), and paratype USNM 498491b (right), all from locality 34. All figures are ×1.

Fig. 121. Prionocyclites mite Kennedy, 1988. A–D. Holotype, USNM 420144, from locality 63.

Fig. 122. External suture of Prionocyclites mite Kennedy, 1988. Holotype, USNM 420144, from locality 63.