Superfamily Crassatelloidea Férussac, 1822
Family Crassatellidae Férussac, 1822
Subfamily Crassatellinae Férussac, 1822
Genus Salaputium Iredale, 1924

Salaputium unicum sp. nov.

Figures 304-310

1992. Salaputium? sp., Kase and Hayami. Jour. Moll. Studies, vol.58, p.448, listed.

Type and material.— Holotype: RM19530a, a living specimen, from the bottom ediments of Fool's Palace" of Shimoji Islet, Miyako Islands. Paratypes: RM19529 (living) from "Devil's Palace", RM19530 (living) from the type locality of Shimoji Islet. RM19531 (living) from "Cross Hole" of Irabu Islet. RM19532 (dead) from "Shodokutsu" of Ie Islet.

Diagnosis.— Small-sized crassatellid, characterized by the truncated posterior area, highly salient umbo, widely spaced and sharp commarginal lamellae, non-crenulated margin, two cardinal teeth and long lateral teeth in each valve, and large hemispherical Pd I.

Description.—Shell very small, rarely exceeding 3.0 mm in maximum length, colorless and opaque, trigonally ovate, weakly convex, about 1.3 times longer than high. Umbonal angle about 130 degrees, comparatively large for crassatellids. Umbo slightly prosogyrous, conically salient, located near mid-length. Antero-dorsal margin long and a little concave; postero-dorsal margin slightly convex, almost rectangularly truncated by posterior margin. Lunule denned by a ridge but very narrow. Surface ornamented with widely spaced and sharp commarginal lamellae, the interval of which is marked with faint growth lamellae. No marginal crenulations. Hinge plate comparatively narrow. Dentition formulated as: (AI) AIII 3a 3b PIII/AII 2 4b PII; 3a rudimentary, 3b rounded triangular, 2 opisthocline, 4b thin and nearly vertical, both lateral teeth elongated along valve margin. Resiliuni adjacent to posterior cardinal tooth. Pd I large, hemispherical, ranging 193-201 µm in maximum diameter; Pd II absent.

Remarks.—Because the posteriorly truncated shell and highly salient umbonal area are unique, the generic reference of the present species is by no means convincing. The hinge structure, however, is almost identical with that of the type species of Salaputuim. No comparable species has been described from Japanese waters.

It is somewhat similar to Crassatella rhomboides Smith, 1885, from the shallow-sea of south New Guinea and near Cape York, but the umbonal angle is much larger, the umbo is more centrally placed, and the interval of commarginal lamellae lacks radial threads. Cotton and Godfrey (1938) regarded three crassatellids from south Australia as belonging to Salaputium. Among others, the specimen of Salaputium micum (Verco, 1895) from the depth of 16-110 fathoms off Fremantle somewhat resembles the present species in outline. The shell-size of the present specimens is, however, much smaller.

Distribution.— Rare in sublittoral caves of Ie, Shimoji and Irabu Islets, Ryukyu Islands.

Superfamily Mactroidea Lamarck, 1809
Family Mesodesmatidae Gray, 1839
Subfamily Erviliinae Dall, 1895

Genus Rochefortina Dall, 1924

Rochefortina has been regarded as belonging to the Mesodesmatidae, but its taxonomic position is still ambiguous, because of the unique hinge structure and microscopically wrinkled and pitted surface. Its type species, Ervilia sandwchensis, was originally described from Hawaii, and has been widely known from the upper sublittoral sandy bottom, of southern Japan, as recorded by Sakurai and Habe (1973).