Thyasiridae, Dall, 1900

Hryniewicz, Krzysztof, Amano, Kazutaka, Jenkins, Robert G. & Kiel, Steffen, 2017, Thyasirid bivalves from Cretaceous and Paleogene cold seeps, Acta Palaeontologica Polonica 62 (4), pp. 705-728 : 722

Thyasiridae gen. et sp. indet. B

Fig. 17B .

Material. — One illustrated specimen ( ZPAL L.16/22; Fig. 17B ) from upper Oligocene cold seep carbonates ( Lincoln Creek Formation ) of SR4 locality, from the Satsop River area, western Washington State, USA .

Description. —Shell quadrangular-oval, 29 mm long, 26.8 mm high. Umbo poorly incurved. Posterior sinus shallow but present, posterior sulcus shallow, broad. Posterior fold high, sculptured by radial ridge running from the umbo towards the posterior end of fold. Surface sculptured by commarginal growth line. Muscle scars unknown.

Remarks.—This specimen resembles smaller individuals of Conchocele taylori in outline and the height of the posterior fold, and C. cf. bathyaulax in the presence of secondary radial ridge amidst posterior fold. However this assignment cannot be confirmed due to the damage of the only specimen available from SR4. More specimens are needed before this species can be assigned to any genus of thyasirids.

Figures

Fig. 17. Thyasiridae gen. et sp. indet A and B, respectively. A. ZPAL L.16/21 from middle to upper Eocene cold seep carbonates of West Fork of Grays River, “Siltstone of Unit B”, western Washington State, USA; a poorly preserved specimen in left lateral view with partially preserved shell. B. ZPAL L.16/22 from an upper Oligocene, SR4 seep carbonate, Satsop River area, Lincoln Creek Formation, western Washington State, USA; a specimen in left left lateral view showing shell outline, external ornament, and secondary ridge running amidst posterior fold (asterisk).