Hoploscaphites plenus (Meek and Hayden, 1860)

Landman, Neil H., Kennedy, W. James, Grier, Joyce, Larson, Neal L., Grier, James W., Linn, Thomas, Tackett, Lydia & Jicha, Brian R., 2020, LARGE SCAPHITID AMMONITES (HOPLOSCAPHITES) FROM THE UPPER CRETACEOUS (UPPER CAMPANIAN – LOWER MAASTRICHTIAN) OF NORTH AMERICA: ENDLESS VARIATION ON A SINGLE THEME, Bulletin of the American Museum of Natural History 2020 (441), pp. 1-131 : 1-131

Hoploscaphites plenus (Meek and Hayden, 1860)

Figures 10C, D, 32C, D , 41–58

Macroconch Synonymy

1860a. Scaphites nodosus var. plenus . Meek and Hayden, p. 177.

1860b. Scaphites nodosus var. plenus . Meek and Hayden, p. 420.

1861. Scaphites nodosus var. plenus . Gabb, p. 33.

1864. Scaphites nodosus var. plenus Meek and Hayden. Meek , p. 24.

1876. Scaphites nodosus Owen var. plenus Meek and Hayden. Meek , p. 429, pl. 26, fig. 1a-c.

?1899. Scaphites nodosus Meek. Logan , p. 209, pl. 22, fig. 2; pl. 23, figs. 1–4, 6–12 (unidentifiable because only sutures and drawings of early ontogenetic stages).

1905. Scaphites nodosus plenus Meek and Hayden. Schuchert , p. 588.

?1905. Scaphites nodosus var. plenus Meek and Hayden. Smith , p. 638, figs. 1.1; 3.4, 7, 8, 10 (unidentifiable because only sutures and early ontogenetic stages).

1916. Scaphites nodosus plenus . Nowak, p. 59.

1927. Acanthoscaphites nodusus var. plenus . Reeside, p. 32.

1933. Scaphites plenus Meek. Elias , p. 314 (pars), pl. 36, fig. 1a-c, 2a-c (unidentifiable because only early ontogenetic stages); pl. 37, fig. 1a-c (unidentifiable because only early ontogenetic stage); pl. 39, fig. 1a-c (unidentifiable because only early ontogenetic stage); pl. 40, figs. 3–5 (unidentifiable because sutures of only early ontogenetic stages), fig. 6 (= Meek, 1876, pl. 26, fig. 1c).

1934. Acanthoscaphites nodosus plenus . Coryell and Salmon, p. 11.

1940. Acanthoscaphites plenus . Landes, p. 178.

1977. Hoploscaphites nodosus plenus (Meek and Hayden) . Kauffman, p. 274, pl. 32, fig. 1 (= Meek, 1876, pl. 26, fig. 1a).

1980. Hoploscaphites nodosus plenus . Thomel, fig. 111.

1983. Jeletzkytes plenus (Meek) . Riccardi, p. 21, pl. 9, figs. 1, 2; text-fig. 13a (= cross section of Meek, 1876, pl. 26, fig. 1a).

?1983. Jeletzkytes aff. brevis (Meek) ♀. Riccardi, p. 27, pl. 6, figs. 1–4; text fig. 23 (suture); text fig. 24 (cross section).

1997. Jeletzkytes plenus (Meek and Hayden, 1860) . Larson et al., p. 80, unnumbered figs.

non 2010. Hoploscaphites plenus (Meek, 1876) . Landman, p. 50, fig 2A, B; p. 198, fig. 86E-G.

2016. Jeletzkytes plenus (Meek and Hayden, 1861) . Klein, p. 143.

Microconch Synonomy

1876. Scaphites nodosus var. quadrangularis Meek , p. 248 (pars), pl. 25, fig. 3a-c only; non fig. 2a-c (= Hoploscaphites brevis microconch); non fig. 4 (= Hoploscaphites crassus microconch).

1910. Scaphites nodosus quadrangularis (Meek) . Grabau and Shimer, p. 177, figs. 1429, 1430 (= Meek, 1876, pl. 25, figs. 3a-c).

1915. Scaphites binodosus F.A. Roemer var. quadrangularis Meek. Frech , p. 559, text-fig. 5.

1921. Scaphites nodosus var. quadrangularis . Grabau, p. 701, fig. 1698h (= Meek, 1876, pl. 25, fig. 3c).

?1931. Acanthoscaphites nodosus var. quadrangularis (Meek and Hayden) . Warren, pl. 1, fig. 2.

1934. Acanthoscaphites nodosus quadrangularis . Coryell and Salmon, fig. 9a, b (= Meek, 1876, pl. 25, fig. 3a, b).

1944. Acanthoscaphites nodosus quadrangularis . Shimer and Shrock, p. 591, pl. 246, figs. 4–6 (= Meek, 1876, pl. 25, fig. 3a-c).

?1968. Scaphites elegans Tate. Jeletzky , p. 49.

1983. Jeletzkytes cf. brevis (Meek, 1876) Ƌ. Riccardi , p. 25 (pars), pl. 10, figs. 5, 6 only (= Meek, 1876: pl. 25, fig. 3a, b),? figs. 10–18;? text-fig. 22b (suture).

1997. Jeletzkytes “ quadrangularis ” (Meek and Hayden, 1860). Larson et al., p. 78, unnumbered fig., lower right (= Meek, 1876, pl. 25, fig. 3a + ventral view).

non 2010. Hoploscaphites plenus (Meek, 1876) . Landman et al., p. 14, fig. 6A–C (= Hoploscaphites crassus microconch).

2010. Hoploscaphites plenus (Meek, 1876) , microconch. Landman et al., p. 14, fig. 6H-K (= Meek, 1876, pl. 25, figs. 3a, b + right lateral + ventral).

EMENDED DIAGNOSIS: Macroconchs medium to large in size, robust; whorl cross section of shaft depressed subquadrate with broadly rounded flanks and venter; width of venter approximately 70% whorl height; small umbilicus; apertural angle averaging 60°; long, fine, straight, closely spaced ribs on adoral part of phragmocone, with little branching or intercalation, and moderately strong adoral projection on venter; long, fine, straight, more widely spaced ribs on shaft, with moderately strong adoral projection on venter; small, closely spaced umbilicolateral tubercles on phragmocone, becoming slightly larger and more widely spaced on body chamber; small, moderately widely spaced ventrolateral tubercles on phragmocone at ⅞ whorl height, becoming much larger and more widely spaced on body chamber, usually persisting to aperture. Microconchs medium to large in size, robust, and more loosely uncoiled than macroconchs; umbilical wall of shaft broad and outwardly sloping; pattern of ornament similar to that of macroconchs, with relatively more prominent umbilicolateral tubercles. Suture deeply incised with broad-stemmed asymmetircally bifid first lateral saddle.

TYPES: Meek and Hayden (1860a: 177) described Scaphites nodosus var. plenus and noted that it differs from Dr. Owen’s [1852] figure of S. nodosus in being greatly more ventricose, and shorter in proportion to its height, whilst the inner row of nodes are much smaller and near the umbilicus. There are some differences in the details of the septa which cannot, however, be readily explained without figures. It is likewise much larger than the specimens represented by Professor Owen, or any individual of that form that we have seen, its length being 4.57 inches, height 3.87 inches, and its breadth 2.52 inches.

The detailed dimensions given by the authors indicate that they were referring to a single specimen, which is, thus, the type by monotypy (USNM 364). Meek (1876: pl. 26, fig. 1a-c) illustrated “the perfect large type-specimen of this variety,” which exactly matches the dimensions given by Meek and Hayden (1860a: 177). It is a steinkern of a macroconch but retains some shell on the adoral end of the phragmocone and body chamber. The right side of the hook exhibits a large reparied injury. It is from the Pierre Shale on the “Yellowstone River, Montana, 150 miles [248 km] above the mouth,” and was collected by Lieutenant G.K. Warren of the U.S. Topographical Engineers. It is probably from the layer of scaphite concretions in the lower Baculites baculus Zone of the Pierre Shale on the Cedar Creek Anticline, Montana ( Bishop, 1967, 1973). Since its initial description, the variety plenus has been elevated to the species level by many authors (e.g., Riccardi, 1983).

The holotype (USNM 366) of Scaphites nodosus var. quadrangularis illustrated by Meek (1876: 428, pl. 25, figs. 3a-c) is a microconch of Hoploscaphites plenus (fig. 56H-K). Together, with the macroconch described above, they form a single dimorphic pair, here desginated as H. plenus .The microconch is from the same locality as the macroconch. It is relatively finely ribbed with widely spaced ventrolateral tubercles. It exhibits a repaired injury on the venter at the point of recurvature, which takes the form of a blister and, as a result, the ribs are more widely spaced in this region.

MATERIAL: The collection consists of 85 complete or nearly complete specimens of which 38 macroconchs and 30 microconchs comprise the measured set. They are most abundant in the Baculites baculus Zone but occasionally occur in the B. eliasi Zone and possibly in the lower part of the B. grandis Zone.

MACROCONCH DESCRIPTION: Adults are medium to large in size. LMAX averages 96.0 mm and ranges from 71.8 to 130.7 mm (table 3). The holotype is on the larger end of the spectrum ( LMAX = 116.2 mm). As in Hoploscaphites crassus , the size distribution is broad with peaks at 85–90 mm and 95–100 mm. Many of the smaller specimens such as BHI 4303 (fig. 49) and BHI 4701 (fig. 50) appear to be from higher up in the stratigraphic section (upper part of the Baculites baculus Zone or possibly lower part of the B. grandis Zone ), but the details needed to confirm this are lacking. The ratio of the size of the largest specimen to that of the smallest is 1.82. The outline of the shell in lateral view is oval. LMAX /HS averages 2.16 and ranges from 2.02 to 2.34 (2.23 in the holotype). YPM 35679 (fig. 53) is an example of a shell with a more rounded outline ( LMAX /HS = 2.02) and AMNH 76294 (fig. 46) is an example of a shell with a more oval outline ( LMAX / HS = 2.34). The shells are relatively tightly coiled with a short shaft and small gap, if any, between the phragmocone and hook. LMAX /HP 2 averages 2.85 and ranges from 2.56 to 3.05 (2.95 in the holotype).

The phragmocone occupies approximately ½ whorl and usually terminates just below the line of maximum length. The apertural angle averages 60° and ranges from 44° to 73° (table 3). The apertural margin is flexuous with a prominent constriction and accompanying varix. The umbilicus is small and deep. The umbilical diameter averages 5.1 mm, and ranges from 3.7 to 6.9 mm. UD / LMAX averages 0.05 and ranges from 0.04 to 0.07 (table 3). The umbilical shoulder of the shaft is straight in side view with a weak umbilical bulge.

The whorl section of the phragmocone at the point of exposure is depressed subquadrate with maximum whorl width at ⅓ whorl height. WP 1 / HP 1 averages 1.10 and ranges from 0.90 to 1.24 (1.23 in the holotype). The umbilical wall is steep and subvertical and the umbilical shoulder is sharply rounded. The flanks are broadly rounded and gently converge toward the venter. The ventrolateral shoulder is sharply rounded and the venter is broadly rounded. In passing from the adapical to the adoral end of the phragmocone, both the whorl width and whorl height increase equally, so that the cross section of the shell, as viewed from the ventral side, does not develop a V-shape, as in Hoploscaphites crassus . The whorl section of the phragmocone along the line of maximum length is only slightly more depressed than that at the point of exposure. WP 2 /HP 2 averages 1.17 and ranges from 0.99 to 1.31 (1.22 in the holotype).

The shell attains its maximum whorl width on the adoral one-third of the shaft, after which the width decreases steadily to the aperture. The shell attains its maximum whorl height at midshaft, after which the height decreases to the point of recurvature and then remains nearly the same up to the aperture. The whorl section at midshaft is depressed subquadrate to reniform. For example, it is subquadrate in YPM 35679 (fig. 53) whereas it is more nearly reniform in the holotype (fig. 42). WS/HS averages 1.09 and ranges from 0.97 to 1.28 (1.20 in the holotype). The umbilical wall of the shaft is steep and subvertical and the umbilical shoulder is sharply rounded. The inner flanks are inflated and well rounded and the outer flanks are more broadly rounded and gently converge toward the venter. The ventrolateral shoulder is sharply rounded and the venter is broadly rounded. VS/HS averages 0.68 and ranges from 0.52 to 0.87 (0.83 in the holotype), indicating that, on average, the venter is not as wide as the whorl is high.

The whorl section becomes more depressed toward the point of recurvature due to a marked decrease in whorl height. WH/HH averages 1.24 and ranges from 1.05 to 1.43 (1.25 in the holotype). The umbilical shoulder is sharply rounded and the flanks are well rounded. The venter is much narrower and more sharply rounded than at midshaft. As in Hoploscaphites crassus , the apertural opening is reduced in size relative to the whorl section at midshaft. It is depressed trigonal in AMNH 76294 (fig. 46) and depressed subovoid in SDSM 149981 (fig. 43).

At the point of exposure, strong ribs arise at the umbilical seam and cross the umbilical wall slightly rursiradiate. They strengthen on the umbilical shoulder and bend slightly backward on the inner flanks and intersect the umbilicolateral tubercles. One rib usually joins an umbilicolateral tubercle dorsally and two or three ribs branch from it ventrally, with one rib intercalating between tubercles. The ribs are straight, moderately widely spaced, and prorsiradiate on the outer flanks with additional intercalation and branching at the ventrolateral tubercles and on the outer margins of the outer flanks. One rib usually joins a ventrolateral tubercle dorsally and two or three ribs branch from it ventrally, with two or three ribs intercalating between tubercles. If the ventrolateral tubercles are paired on opposite sides of the venter, ribs that branch from a tubercle on one side of the venter loop to a tubercle on the opposite side. Ribs are uniformly strong and evenly spaced on the venter, which they cross with a moderately strong adoral projection. In the holotype, the rib density on the venter is 6 ribs/cm on the adapical end of the phragmocone.

On the adoral end of the phragmocone, ribs are narrow and slightly rursiradiate on the umbilical wall. They strengthen on the inner flanks and pass between or merge with the umbilicolateral tubercles. In the holotype, one or two ribs join an umbilicolateral tubercle dorsally and two or three ribs branch from it ventrally, with one or two ribs intercalating between tubercles. The outer flanks are covered with long, narrow, closely spaced, rectiradiate ribs, a pattern that this species shares in common with Hoploscaphites crassus and H. peterseni . Intercalation and branching occur on the outer margins of the outer flanks and at the ventrolateral tubercles. In the holotype, groups of four or five ribs branch from each ventrolateral tubercle and link to tubercles on the opposite side of the venter, with as many as five nontuberculate ribs intercalating between tubercles. Ribs cross the venter with a moderately strong adoral projection. The rib density on the venter on the adoral part of the phragmocone ranges from 6 to 8 ribs/cm (6 ribs/cm in the holotype).

On the shaft, ribs cross the umbilical wall with a slight backward bend. In YPM 35679 (fig. 53), 9 ribs/cm are present on the umbilical wall. They strengthen on the umbilical shoulder and are concave on the inner flanks. Due to poor preservation of this specimen, it is difficult to determine the exact number of ribs that join and branch from each umbilicolateral tubercle. The best estimate is that one or two ribs join an umbilicolateral tubercle dorsally and two or three ribs branch from it ventrally. Ribs are straight and weakly prorsiradiate on the flanks, becoming more strongly prorsiradiate adorally. In the holotype, four or five ribs join a ventrolateral tubercle dorsally and six or seven ribs branch from it ventrally, with as many as eight ribs intercalating between tubercles. Because tubercles are offset on opposite sides of the venter in the holotype, the ribs that branch from a tubercle on one side of the venter intercalate between pairs of tubercles on the opposite side of the venter. Ribs cross the venter with a moderately strong adoral projection. The rib density on the venter ranges from 5 to 8 ribs/cm (6 ribs/cm in the holotype).

As on the shaft, the ribs on the flanks of the hook are straight and prorsiradiate. The ribbing on the holotype is interrupted by an injury on the right side (fig. 42). As a result, the ribs are strongly convex on the flanks and bend backward at the ventrolateral margin, which is devoid of ornament. In contrast, the ornament on the left side of the shell is undisturbed. In all specimens, ribs cross the venter with a moderately strong adoral projection. In general, the ribs on the hook are slightly more closely spaced than those on the shaft (6 ribs/cm on the venter of the shaft versus 7 ribs/cm on the venter of the hook in the holotype).

Small, closely spaced umbilicolateral tubercles are present on the phragmocone in most, but not all, specimens. They occur at ⅓ whorl height. The tubercles are more or less evenly spaced, becoming slightly more widely spaced toward the adoral end of the phragmocone. The maximum distance between consecutive tubercles ranges from 4 to 5.5 mm (4.5 mm in the holotype). A total of 11 umbilicolateral tubercles are present on the phragmocone of the holotype. The tubercles are bullate in shape and radially elongate, with a maximum height of 1 mm.

If umbilicolateral tubercles are present on the phragmocone, they usually extend onto the body chamber, but not necessarily to the aperture. They are surprisingly weak relative to the much stronger ventrolateral tubercles. They occur at ⅓ whorl height and become more widely spaced adorally, with the maximum distance between consecutive tubercles ranging from 10 to 17 mm (17 mm in the holotype). A total of 4 umbilicolateral tubercles are present on the body chamber of the holotype, so that the total number of umbilicolateral tubercles on the exposed shell of this specimen is 14. The tubercles are bullate in shape with a maximum height of 2 mm.

Ventrolateral tubercles are present at the point of exposure and continue onto the entire exposed phragmocone. They occur at ⅞ whorl height and are perched either on the ribs or in the interspaces between them. Tubercles may be paired or offset from one side of the venter to the other. A total of 11 ventrolateral tubercles are present on the phragmocone of the holotype. Tubercles are more or less evenly spaced, becoming more widely spaced toward the base of the body chamber. The distance between the two most adoral tubercles in the holotype is 13 mm. Tubercles are conical in shape and slightly elongated radially. They range in height from 1.25–2.25 mm.

The ventrolateral tubercles on the body chamber also occur at ⅞ whorl height and are paired or offset on opposite sides of the venter. They are widely spaced with the maximum distance between consecutive tubercles occuring on the adoral end of the shaft, after which they become slightly more closely spaced on the hook and usually, but not always, persist to the aperture. We describe the spacing of tubercles in three specimens to illustrate the range of variation. In the holotype (fig. 42), the distance between tubercles increases from 19 mm on the adapical end of the shaft to 30 mm on the adoral end of the shaft, and then decreases to 25 mm on the hook. In AMNH 76294 (fig. 46), which is a slightly smaller specimen, the distance between tubercles on the shaft remains nearly the same throughout (14–16 mm), and then gradually decreases to 8.5 mm near the aperture. In AMNH 135090 (fig. 47), which is nearly the same size as AMNH 76294, the distance between tubercles on the shaft also remains nearly the same throughout (17–20 mm), and then gradually decreases to 7 mm near the aperture.

In addition to their wide spacing, one of the characteristic features of the ventrolateral tubercles is their large size. They reach a maximum size on the adoral end of the shaft and beginning of the hook, after which they diminish in size or disappear. They are clavate in shape with steeply sloping adapical faces and gently sloping adoral faces. Where preserved in their entirety, or nearly so, tubercles range from 2 to 6 mm in height and up to 11 mm in length. Commonly, however, the tubercles are broken off and only their bases remain.

As a result of their large size and wide spacing, the number of ventrolateral tubercles on the shell is lower than that in the closely related species Hoploscaphites crassus . For example, the total number of ventrolateral tubercles on the exposed shell of the holotype of H. plenus is 19 (fig. 42). The total number of tubercles on the exposed shell of BHI 4701 is 18 (fig. 50) and the total number of tubercles on the exposed shell of AMNH 105910 is 23 (fig. 44). In contrast, the total number of ventrolateral tubercles on the exposed shell of the holotype of H. crassus is 30 (fig. 13).

Lateral tubercles are rare or absent in all of the specimens in our collection. The holotype bears slightly bullate swellings, three in number, starting at the point of exposure, on the left side of the shell. They occur near the ventrolateral tubercles on the outer one-third of the flanks. The maximum height of the swellings is 0.5 mm and the maximum distance between them is 6.5 mm. The swellings disappear toward the middle one-third of the exposed phragmocone.

The suture is deeply incised (fig. 32C; Meek, 1876: pl. 26, fig. 1c; Elias, 1933: pl. 40, fig. 6). The first lateral saddle is broad stemmed and asymmetrically bifid. The first lateral lobe (L) is narrow, symmetrically bifid, and not as deep as the ventral lobe.

MICROCONCH DESCRIPTION: What we interpret as microconchs of this species are robust, loosely uncoiled forms, with relatively flat flanks and widely spaced ventrolateral tubercles on the body chamber. Adults are small to medium in size. LMAX averages 58.5 mm and ranges from 51.1 to 68.2 mm (table 4). The size distribution is unimodal with a peak at 60–65 mm (fig. 41). The ratio of the average size of microconchs to that of macroconchs is 0.61.

UD averages 3.8 mm and ranges from 3.0 to 4.7 mm (table 4). UD / LMAX averages 0.06 and ranges from 0.06 to 0.08. The average value in microconchs is higher than that in macroconchs (0.05). The umbilical shoulder is concave in lateral view in contrast to macroconchs in which it is straight or convex in lateral view. Microconchs are oval in side view and more loosely uncoiled than macroconchs. LMAX /HP 2 averages 3.02, which is significantly higher than that in macroconchs (2.85). The phragmocone is relatively large and represents approximately 60% of the shell length and usually terminates below the line of maximum length.

The whorl section at the point of exposure is subovoid and nearly equidimensional, with maximum whorl width at ¼ whorl height. WP 1 /HP 1 averages 1.02 and ranges from 0.74 to 1.30. The umbilical wall is steep and subvertical, and the umbilical shoulder is sharply rounded. The inner

LMAX (mm)

flanks are well rounded and the outer flanks are broadly rounded and gently converge toward the venter. The ventrolateral shoulder is sharply rounded and the venter is broadly rounded.

Whorl width expands into the body chamber and attains its maximum value at the point of recurvature. Whorl height also increases, and attains its maximum value at midshaft, after which it remains the same. The whorl section at midshaft is depressed reniform with maximum whorl width at ⅓ whorl height. WS/HS averages 1.11 and ranges from 0.88 to 1.30 (table 4). The umbilical wall is broad and slopes outward, and the umbilical shoulder is sharply rounded. The inner flanks are well rounded and the outer flanks are broadly rounded. The ventrolateral shoulder is sharply rounded and the venter is broadly rounded. VS/HS averages 0.74 and ranges from 0.59 to 0.90, indicating that, on average, the venter is approximately ¾ as wide as the whorl is high. The whorl section at the point of recurvature is more ovoid and depressed than that at midshaft. WH/HH averages 1.19 and ranges from 1.02 to 1.36. The apertural opening is approximately the same size as the whorl section at midshaft, unlike the situation in macroconchs in which the apertural opening is reduced relative to that at midshaft.

The ornament in microconchs is similar to that in macroconchs. On the exposed phragmocone, ribs arise at the umbilical seam and are strong and rectiradiate on the umbilical wall. They swing backward on the inner flanks, forward on the midflanks, and backward again on the outer flanks. Intercalation and branching occur almost exclusively at the umbilicolateral and ventrolateral tubercles. One rib usually joins an umbilicolateral tubercle dorsally and two ribs branch from it ventrally, with one rib intercalating between tubercles. One or two ribs join a ventrolateral tubercle dorsally and as many as four ribs branch from it ventrally, with one or two ribs intercalating between tubercles. Ribs are strong and uniformly spaced on the venter, which they cross with a moderately strong adoral projection. The rib density on the adoral part of the phragmocone is 8 or 9 ribs/cm.

Figures

FIGURE 32. Sutures of Hoploscaphites crassus (Coryell and Salmon, 1934), H. plenus (Meek and Hayden 1860), and H. peterseni. A. Hoploscaphites crassus, AMNH 76167, microconch, second from last suture, H = 22.1 mm, AMNH loc. 3921, lower Baculites baculus Zone, Pierre Shale, Cedar Creek Anticline, Montana. B. Hoploscaphites crassus, AMNH 76166, microconch, fourth from last suture, H = 21.5 mm, AMNH loc. 3921, lower Baculites baculus Zone, Pierre Shale, Cedar Creek Anticline, Montana. C. Hoploscaphites plenus, macroconch, BHI 4130, second from last suture, AMNH loc. 3921, Baculites baculus or lower B. grandis Zone, Pierre Shale, Cedar Creek Anticline, Montana. D. Hoploscaphites plenus, microconch, YPM 35597, second from last suture, W = 18.4 mm, Baculites baculus or lower B. grandis Zone, Pierre Shale, Wibaux (= Mingusville), Montana. E. Hoploscaphites peterseni, macroconch, AMNH 76187, last suture, AMNH loc. 3921, lower Baculites baculus Zone, Pierre Shale, Cedar Creek Anticline, Montana.

FIGURE 41. Size frequency histogram of Hoploscaphites plenus (Meek and Hayden, 1860), based on the samples in tables 3 and 4.

FIGURE 42. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. USNM 364, cast of holotype, unknown locality, but probably Baculites baculus or lower B. grandis Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 43. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. SDSM 149981, upper Baculites eliasi or lower B. baculus Zone, Pierre Shale, Dawson County, Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 44. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. AMNH 105910, AMNH loc. 3921, upper Baculites baculus Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 45. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A, B. AMNH 135966, AMNH loc. 3921, lower Baculites baculus Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, ventral; B, left lateral. C, D. BHI 4130, Baculites baculus or B. grandis Zone, Pierre Shale, Cedar Creek Anticline, eastcentral Montana. C, ventral; D, left lateral.

FIGURE 46. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. AMNH 76294, loc. 3921, upper Baculites baculus Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 47. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. AMNH 135090, unknown locality. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 48. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. AMNH 71856, AMNH loc. 3921, upper Baculites baculus or lower B. grandis Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 49. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. BHI 4303, Baculites baculus or lower B. grandis Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 50. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. BHI 4701, Baculites baculus or lower B. grandis Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.

FIGURE 51. Hoploscaphites plenus (Meek and Hayden, 1860), macroconch. A–D. AMNH 76189, AMNH loc. 3921, Baculites baculus or lower B. grandis Zone, Pierre Shale, Cedar Creek Anticline, east-central Montana. A, Right lateral; B, apertural; C, ventral; D, left lateral. Arrow indicates the base of the body chamber.