Shell large, thin, greyish, with a velvety periostracum, equivalve, inequilateral, inflated; beaks low, rather anterior; posterior end compressed, pointed, attenuated; anterior end evenly rounded; posterior dorsal slope descending, nearly straight, base roundly arcuated; hinge with an internal resilium inclined posteriorly, and a single long lateral tooth in the right valve; length of shell, 25; beaks before posterior end, 15; height, 16; diameter, 11 mm. U. S. Nat. Mus. Cat. No. 110770.
Dredged at station 4992, in the Japan Sea, in 325 fathoms, mud, by the United States Bureau of Fisheries steamer Albatross.
This belongs to the typical section of the genus, and is notable for its thick velvety periostracum.

Cuspidaria trosaetes is a delicate, medium-sized cuspidariid from the Japan Sea, ranging from Hyogo Prefecture to Hokkaido, Japan (and maybe the Kuril Islands). Like other members of Cuspidaria, it is a truly carnivorous and predatory bivalve that actively hunts small crustaceans (such as copepods and ostracods) using its inhalent siphon and trapping them in the mantle cavity. It inhabits a rather wide bathymetric range of around -50~650m, and is usually found on soft bottoms. It is characterised by a short, compressed posterior rostrum and a well inflated oval shell. The shell itself is white, with a greenish-brown periostracum which is thin and semi-transparent at first but increasingly thickens and as a result becomes more opaque in later stages. A rare species, it is very difficult to obtain a live-taken specimen in good condition. Typical shell length around 30mm., very large specimens may exceed 40mm.