86 CONCHOLOGIA CESTRICA. 



Family UNIONID^E. 



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.E. 



GENUS. 



UNIO. 



SPECIES. 

 complanatus, 

 radiatus, 

 cariosus, 

 ochraceus, 

 Fisherianus, 

 nasutus, 

 heterodon. 



I" margaritifera, 

 MARGARITANA. < undulata, 



( marginata. 



f fluviatilis, 



FAMILY. 



UNIONID^E. 



(^ Tryonii. 



Genus UNIO, RETZIUS, 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; branchiae 

 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. 



