The shells of this genus are very small, and are found buried in the mud
of fresh waters; the apices or summits are never eroded, and some
species are so thin as to be transparent.
Shell covered with a brown epidermis, oval or sub-orbicular, regular,
equivalve, inequilateral; summits blunt, contiguous, or turned
anteriorly; hinge similar, complex, formed by a variable number of
cardinal teeth, and by two remote lateral teeth with a cavity at the
base; ligament exterior, posterior, and convex; two distant muscular
impressions, without posterior sinus.
Cyclas rivicola.
C. cornea.
C. lacustris.
C. obliqua.
C. calyculata.
C. obtusalis.
C. fontinalis.
C. Australis.
C. sulcata.
C. striatina.
C. Sarratogea.
_C. cornea._ The horny Cyclas. Pl. 9, fig. 7.
Species sub-orbicular, convex, thin, pellucid, with fine concentric
striæ; cardinal teeth a little variable, always very small, and
sometimes obsolete; summits not eroded, covered with a horn-coloured
epidermis; interior bluish white.