Paskentana hamiltonensis, Kaim, Andrzej, Jenkins, Robert G., Tanabe, Kazushige & Kiel, Steffen, 2014

Kaim, Andrzej, Jenkins, Robert G., Tanabe, Kazushige & Kiel, Steffen, 2014, Mollusks from late Mesozoic seep deposits, chiefly in California, Zootaxa 3861 (5), pp. 401-440 : 420-421

Paskentana hamiltonensis sp. nov.

( Fig. 8 F–G)

Type locality and strata: Bear Creek, Colusa County, California, USA. The locality # 4 in Kiel et al. (2008b); Great Valley Group, Grizzly Canyon member of Crack Canyon Formation; Valanginian (Early Cretaceous).

Holotype: GZG.INV.84991, a shell with well preserved ornamentation, 18.1 mm high and 16.1 mm wide.

Paratype: GZG.INV.84992 with partially preserved aperture, 21.3 mm high and 18.0 mm wide.

Diagnosis. Shell broad turbiniform, strongly convex and angular in the middle of the whorl. Angulation equipped with narrow and tall band-like keel. Spiral ribs numerous (more than 15 on the last whorl), smooth. Aperture uninterrupted but narrowing anteriorly.

Description. The shell is broad turbiniform with at least four teleoconch whorls. Whorls are strongly convex and angular in the middle of lateral flank. The angulation is underlined by a narrow and tall band-like keel. The suture is distinct, incised; number of spiral cords per whorl increases from 10 on early whorls to more than 15 on later ones, new spiral cords appear gradually between earlier ones; no nodules at the intersections of spiral cords and fine prosocline growth lines. The same sculpture present on the whorl base. Aperture D-shaped uninterrupted but slightly pointed anteriorly.

Remarks. Paskentana hamiltonensis sp. nov. differs from all other Paskentana species by having a clear median angulation of the whorls equipped with strong band-like keel; this feature is visible even in juvenile specimens. Paskentana berryessaenis Kiel et al. 2008b , which is also slightly angulated, additionally has a clear nodular pattern at the intersections of spiral ribs and growth lines, and fewer spiral ribs. Moreover, the aperture of P. hamiltonensis is pointed anteriorly while in P. berryessaenis it is continuously circular. It remains uncertain whether the specimen from Bear Creek illustrated by Kiel et al. (2008b: fig. 7C) as P. berryessaensis belongs to the latter or rather to P. hamiltonensis because of the imperfect preservation of the specimen.

Etymology. The type locality is located near the mouth of Hamilton Canyon.

Figures

FIGURE 8. A – C, E, J. Paskentana humerosa (Stanton, 1895) from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA. A. GZG. INV. 84987. B. GZG. INV. 84988. C. GZG. INV. 84989. E, J. Juvenile GZG. INV. 84990. D, I. Atresius liratus Gabb, 1869 from? Valanginian (Early Cretaceous) seep carbonates at Rocky Creek, Lake County, California, USA; juvenile GZG. INV. 84993. F – G. Paskentana hamiltonensis sp. nov. from from Valanginian (Early Cretaceous) seep carbonates at Bear Creek, Colusa County, California, USA. F. Paratype (GZG. INV. 84992). G. Holotype (GZG. INV. 84991). H. Paskentana globosa Kiel et al., 2008 from Tithonian (Late Jurassic) seep carbonates at Paskenta, Tehama County, California, USA; GZG. INV. 84986.