86 CONCHOLOGIA CESTRICA. 
Family UNIONIDE. 
Shell, transverse, inequilateral, covered with an epi- 
dermis; hinge with a simple, or divided, cardinal tooth 
in front, and a lamellar one running back beneath the 
ligament; sometimes the lamellar tooth is wanting; and 
sometimes both are absent. 
Animal, mantle open beneath, its edges thickened, 
often fringed; tubes two, the vent tube above; foot 
thick, compressed, muscular, coriaceous. 
DIAGRAM OF THE GENERA, AND SPECIES, OF THE FAMILY 
UNIONID. 
FamI_y. GENUS. SPECIES. 
complanatus, 
P radiatus, 
Cariosus, 
ochraceus, 
Fisherianus, 
nasutus, 
UNIONID. heterodon. 
margaritifera, 
MARGARITANA. undulata, 
’ marginata. 
Unio. 
{ fluviatilis, 
ANODONTA. J implicata, 
edentula, 
Tryonii. 
Genus UNIO, Rerzius, 1788. 
Shell, transverse, with three deeply-impressed cica- 
trices; thick, or thin and fragile; teeth varying, or 
absent. 
Animal, the mouth lips wider than long, united for 
two-thirds on the upper margin; mantle open; branchiz 
four, the outer free posteriorly, and lies in a fold of the 
mantle; the inner are united to the foot anteriorly, the 
remainder free; foot tongue-shaped, and produced 
anteriorly. 
Unio complanatus, SOLANDER. 
Myacomplanata, Solander, MSS. Portland Cat. in Brit- 
ish Museum. Unio purpureus, Say, Barnes, and others. 
