Maorithyas

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 : 720

Maorithyas ? sp.

Fig. 14 .

Material.— One specimen ( ZPAL L.16/13) from the upper Eocene Bear River site from the “Siltstone of Cliff Point” in western Washington State, USA .

Remarks.—The specimen from the Bear River site is incomplete and weathered, therefore its systematic assignment is only tentative. Its inflated shell and very shallow posterior sulcus somewhat resembles that of Maorithyas humptulipsensis from the middle Eocene Humptulips River site in Washington State. However, the Bear River specimen is 21 mm long and shorter than the majority of the specimens of Maorithyas humptulipsensis available for comparison. Also, it has a somewhat less pronounced posterior fold than M. humptulipsensis , and a less pronounced umbo, suggesting that the Bear River specimen does not belong to M. humptulipsensis . Any further discussion of the Bear River species has to be postponed until more material from this locality is available.

Genus Thyasira Lamarck, 1818

Type species: Thyasira flexuosa ( Montagu, 1803) ; Recent , Falmouth Harbour, Cornwall, UK .

Figures

Fig. 14. Thyasirid bivalve Maorithyas? sp. from upper Eocene cold seep carbonates in the “Siltstone of Cliff Point”, Bear River, western Washington State, USA. ZPAL L.16/13, a poorly preserved specimen in left (A), right (B) lateral, and dorsal (C) views.