Family Callochitonidae Thiele, 1910.

Callochiton chattonensis n. sp. (Figs. 13a, 13b).

There were two minute median valves of a new Callochiton in the collection labelled “Ischnochiton? sp.”; one, herein described, is in a good state of preservation, the other, unfortunately now lost, was very imperfect, although the sculptural characters were sufficient to identify it.

Both valves were more strongly carinated than C. platessa, the angle of divergence being 100°; the holotype. measures 1.75 × .75 mm., the other valve 1.60 × .50 mm.

Upper side.—The dorsal area is broadly wedge-shape, smooth except for megalopores, bluntly beaked, anterior margin strikingly bowed forward. Under 62 mag. the pleural area is seen to be ornamented with about 10 rows of subgranulose, longitudinal ridges, which are separated from the adjoining row by a string of circular pits, giving to the shell, when seen under this power, a honeycomb appearance which, although shallow, is distinctive; the lateral area is raised but the honeycomb sculpture of the pleural area is absent, a few circular granules are irregularly present, the whole surface of the shell is minutely rugose; two ill-defined growth-ridges are discernible.

Inside.—White, callus strong, eaves over-hanging, spongy, insertion-plate complete on one side, teeth sharply edged, slits three; the tegmentum is folded over into the inside along the whole posterior margin of valve, the sutural laminae incomplete, shallow, the sinus between very broad and much bowed forwards.

Locality.—Chatton, near Gore, Southland (Ototaran, Oligocene).