3. Anodonta. Fifteen species.
A fresh-water shell, found in ponds and lakes, difficult to be distinguished from the Unio but by the hinge, which wants the cardinal and lateral tooth, and merely presents a smooth internal rim round the edge terminated by a sinus or notch, in which the anterior extremity of the ligament is sunk; the substance is pearly, covered with a false epidermis.
Shell ordinarily rather thin, regular, close, equivalve, inequilateral; summit anterodorsal; hinge linear, without teeth; ligament external, dorsal, and post-apicial; two well-marked muscular impressions.
Anodonta cygnæa.
A. anatina.
A. sulcata.
A. fragilis.
A. cataracta.
A. trapezialis.
A. exotica.