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.
A. rubens.
A. crispata.
A. uniopsis.
A. Pennsylvanica.
A. intermedia.
A. glauca.
A. sinuosa.
A. Patagonica.
_A. cygnæa._ The Swan Anodonta. Pl. 11, fig. 2.
Species oval, thin, elongated, hinge straight, and only auriculated
anteriorly; beaks small and ventricose; concentrically wrinkled; covered
with a greenish epidermis, which is frequently of a brown tinge towards
the umbo.
_A. rubens._ The ruddy Anodonta.
Species oval, hinge arched, without trace of auricula or ear.
_A. trapezialis._ The trapezium Anodonta. Pl. 11, fig. 3. Species oval
or rounded, auriculated on both sides the summit.