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. A

Fig. 17A .

Material. — One illustrated specimen ( ZPAL L.16/21; Fig. 17A ) from middle to upper Eocene cold seep carbonates of the “Siltstone of Unit B” from the West Fork of Grays River, western Washington State, USA .

Description. —Shell ovate, the available specimen is 18.9 mm long and 19.3 mm high with preserved surface covered with fine commarginal growth lines. Sulcus well visible, moderately deep and straight. Umbo poorly incurved. Anterior and posterior adductor muscle scars unknown.

Remarks.—This species is in rather poor condition and we leave it in open nomenclature. It could represent a juvenile specimen of an unidentified species of Conchocele (e.g., Kharlamenko et al. 2016: fig. 4D–F), a specimen of an unidentified species of Maorithyas or of Thyasira .

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).