Cibolaites sp. Kaplan, 1988: 23

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 : 34-41

Cibolaites sp. Kaplan, 1988: 23 , pl. 6, figs. 4, 5. Cibolaites molenaari Cobban and Hook. Cobban

and Hook, 1989: figs. 8c, d.

Cibolaites molenaari Cobban and Hook, 1983 .

Reyment and Kennedy, 2001: fig. 1a, b.

TYPES: Holotype is USNM 328766 (fig. 5), from the Rio Salado Tongue of the Mancos Shale, lower Turonian Mammites nodosoides Zone , immediately below the first occurrence of Collignoniceras woollgari woollgari of the middle Turonian at USGS Mesozoic locality D11208, NE1/4 sec. 36, T. 6 N, R. 19 W, Cibola County, New Mexico. Paratypes USNM 328752–328767, 329013, are from the Rio Salado Tongue at this and nearby localities.

DIAGNOSIS: Characteristic features of this moderate­size species are the strong, nodate umbilical tubercles during early and middle growth and the equal numbers of prominent siphonal clavi and clavate inner ventrolateral tubercles.

DESCRIPTION: The early whorls are smooth to a diameter of 5 mm, with rounded flanks and venter. Low umbilical bullae, 14 per whorl, appear between 5 and 7 mm diameter; ventrolateral and siphonal tubercles appear around 10 mm diameter. As size increases (figs. 6, 7), the number of bullae decreases to as few as seven per whorl in middle growth. Coiling is fairly involute, with a deep umbilicus. Two broad prorsiradiate to rectiradiate ribs generally arise from each bulla, which vary in strength within and between specimens. The ribs are broad, round­ ed, and terminate in strong ventrolateral cla­ vi; occasional intercalated ribs arise around midflank or below and bear clavi of comparable strength to give a total of 22 or so ribs per whorl at diameters of up to 65 mm. Each ventrolateral clavus gives rise to a broad, low prorsiradiate rib that arches forward across the venter to form an obtuse chevron with a strong siphonal clavus at the apex. In profile, the adapical slope of this clavus is low, the adapertural slope much steeper, giving the clavus a distinctly asymmetric profile. At this stage the costal and intercostal whorl sections vary from compressed to depressed (see table 1); the greatest breadth in intercostal section is just outside the umbilical shoulder. The inner flanks are broadly rounded, the outer flanks flattened and convergent, and the venter fastigiate. The costal section has the greatest breadth at the umbilical bullae and the flanks are concave between tubercles; the venter is markedly fastigiate. On the later parts of the phragmocone as well as on the adult body chamber, the ornament is progressively modified (fig. 5); first, the umbil­ ical bullae decline and ultimately disappear. The ventrolateral and siphonal clavi weaken markedly, but are still present, though very weak, immediately adapical of the adult aperture. As they decline, the venter broadens and rounds. On the body chamber, the flanks flatten and the whorl section becomes rectangular, with low, weak, prorsiradiate ribs, irregularly long and short, the latter of variable length. Part or all of the body chamber is preserved on 46 specimens. Diameter at the last septum ranges from 44 to 94 mm, without any clear clustering into size classes or indication of size dimorphism. Suture with broad, bifid E/L, narrow, bifid L, slightly broader L/U 2, and much narrower U 2 (fig. 8).

Cibolaites molenaari occurs as gracile and robust forms, as indicated in the figure captions, although the distinctions between them are not as pronounced as in species of Collignoniceras and Prionocyclus . The holotype and paratypes figured by Cobban and Hook (1983) can be assigned to the following forms: gracile form, pl. 2, figs. 1–6, pl. 3, figs. 3, 4, 6–8, pl. 14, figs. 1–15; robust form, pl. 2, figs. 7–9, pl. 3, fig. 5, pl. 8, figs. 6–8, pl. 13, figs. 1–5.

DISCUSSION: Coarse ornament and presence of only a single row of ventrolateral tubercles at all stages distinguishes C. molenaari from all of the collignoniceratids described here. Body chamber characters sep­

TABLE 2 Dimensions of Collignoniceras woollgari regulare (Haas, 1946) a

arate it from Lecointriceras fleuriausianum (D’Orbigny, 1841) (fig. 9) as discussed above.

OCCURRENCE: Upper Cenomanian Neocardioceras juddii Zone in Devon, England, and Aube, France; lower Turonian Mammites nodosoides Zone in west­central New Mexico and northeastern Arizona; N.W. Germany.