Astarte trapezoidalis, (Stanton, 1895)

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 : 430-431

Oxyeurax trapezoidalis ( Stanton, 1895)

( Fig. 16 )

Astarte trapezoidalis Stanton 1895 , p. 57–58, pl. 6, figs. 17–18.

Supplementary description. Anterior adductor muscle scar slightly oval, pedal retractor scar small and round and separated from the adductor muscle scar. The pallial line is entire; on the interior of the anteroventral side of the shell, several radial grooves appear near the pallial line, run across it, but fade before reaching the margin. The posterior adductor muscle scar is indistinct. At the posterodorsal margin of the shell, the fine commarginal sculpture stops at the sharp crest that forms the edge of the escutcheon; the interior of the escutcheon is smooth. The ligament is short and reaches only about a third of the length of the escutcheon.

Material and occurrence. 27 specimens from Bear Creek (Valanginian, Early Cretaceous), 58 from Rocky Creek (probably Valanginian, Early Cretaceous) and one from Eagle Creek (Late Barremian, Early Cretaceous); Stanton’s type material from Knoxville and Reiff, two localities in the general area of Rocky Creek, was also investigated ( USNM 23104).

Remarks. Stanton (1895, p. 58) noted that ‘internal casts (from another locality) show impressions of the hinge, which also seem to agree with it [its position within Astarte ]’. The mentioned internal cast was found among Stanton’s type material (USNM 23104) and is from ‘Knoxville, near Reiff P.O., 1 mile N.W. of Palmer’s ranch, Morgan Valley’ ( Stanton 1895, p. 58), which is to the south of the Rocky Creek site; this specimen shows two cardinal teeth in each valve and is illustrated here ( Fig. 16 D). A similarly elongate species with an anterior umbo is Oxyloma cyphopleura Gardner & Campbell, 2002 from the Middle Temaikan (Bajocian–Bathonian) Tucks Bay Formation in South Otago, New Zealand ( Gardner & Campbell 2002, p. 38, fig. 32).

Figures

FIGURE 16. Oxyeurax trapezoidalis (Stanton, 1895) from Cretaceous seep carbonates in California. A. Left valve showing the anterior adductor muscle scar, from Bear Creek (GZG. INV. 85007). B. Dorsal view on a specimen from the Valanginian of Bear Creek showing pedal retractor scars and the sharply delineated escutcheon (GZG. INV. 85008). C. Juvenile specimen with more oval shell shape and regular ornament, from Bear Creek (GZG. INV. 85009). D. Dorsal view on specimen from Stanton’s type series (USNM 23104) showing the outline of the hinge dentition, from the ‘ Reiff’ locality. E-G. Holotype (USNM 23104), from Knoxville.