The species of this genus become every day more numerous; they are found
in all countries, but particularly in North America. The Unio is a
fresh-water shell, and therefore, with great propriety, removed from the
Mya, which consists entirely of marine shells. The substance is pearly;
the exterior covered with a brown or green epidermis; the apices eroded.
They are found in the mud of rivers, with their apices downward; some
are slightly gaping, and some species produce fine pearls.
Shell generally very thick, pearly within, covered with epidermis;
summits eroded, dorsal, and sub-interior; besides a long lamellous tooth
under the ligament, the hinge is formed by a double precardinal tooth,
more or less compressed, and dentated irregularly on the left valve,
simple on the right valve; ligament external, dorsal, and post-apicial;
muscular impressions well marked.
Unio sinuata.
U. elongata.
U. crassidens.
U. Peruviana.
U. rariplicata.
U. pupurata.
U. ligamentina.
U. obliqua.
U. retusa.
U. rarisulcata.
U. coarctata.
U. purpurascens.
U. radiata.
U. brevialis.
U. rhombula.
U. carinifera.
U. Georgina.
U. clava.
U. recta.
U. naviformis.
U. glabrata.
U. nasuta.
U. ovata.
U. rotundata.
U. littoralis.
U. semirugata.
U. nana.
U. alata.
U. deladonta.
U. sulcidens.
U. rostrata.
U. pictorum.
U. Batava.
U. corrugata.
U. nodulosa.
U. varicosa.
U. granosa.
U. depressa.
U. Virginianum.
U. luteola.
U. marginalis.
U. angusta.
U. manca.
U. cariosa.
U. spuria.
U. Australis.
U. anodontina.
U. sub-orbiculata.
_U. pictorum._ The Painter’s Unio. Pl. 8, fig. 6.
Species oval, not auriculated, strong, anterior side rhomboid and
attenuated; the opposite side obtusely acute; the umbones somewhat
warted; concentrically wrinkled; covered with a dusky green epidermis.
_U. sinuata._ The crooked Unio.
Species oval, sub-auriculated; cardinal tooth short, not lamellar or
sub-striated.
_U. sub-orbiculata._ The sub-orbicular Unio.
Species round or almost round; cardinal tooth compressed, elongated, and
often lamellar.