Subgenus Notirus Finlay, 1928

Irus (Notirus) sp. indet.

Figures 355-364

This species is represented by a living specimen (RM19558) from the bottom sediments of "Cross Hole" of Irabu Islet as well as several empty valves from "Devil's Palace" (RM19557) of Shimoji Islet, Miyako Islands, and from "Shodokutsu" (RM19559) of Ie Islet, Okinawa.

The shell is very small, about 3 mm long, about 1.4 times longer than high, pale pink, regularly subquadrate with truncated posterior margin, not strongly inflated, possessing nearly straight ventral margin, a distinct lunule and highly raised commarginal lamellae. Hinge is veneroid, consisting of three cardinal teeth and a pair of lateral teeth in each valve. Pd I is small, and Pd II is distinct.

The outline of the present species is somewhat similar to the juvenile stage of Irus ishibashianus Kuroda and Habe, 1952 [= Venerupis irus (Linnaeus) sensu Yokoyama, 1924] which was referred to Notirus by Oyama (1973). The commarginal lamellae, however, are more densely spaced, and their interspaces are almost free from radial threads. In the subquadrate outline it somewhat resembles Venerupis reflexa Gray, 1843, from New Zealand, the type species of the subgenus Notirus, but the shell is much smaller and the ventral margin is not arcuate in the present species.