482 HISTORY OP 



H. palliatal H. fuliginosa ; H. hirsuta ; H. pulchella; H. in- 

 dentata ; H. electrinal H. labyrinthica. 



1 have found Succinea obliqua upon the islands in the Sus- 

 quehanna, opposite to Washington. The shell presents a 

 strong resemblance to some of the forms of Limnea colum- 

 ella, a species which will probably be detected hereafter in 

 this county, as it occurs in other parts of the state, as in the 

 Ticinity of Philadelphia, and in York county. 



Unionid^. 



This family includes all our large bivalve shells, usually 

 called mussles. 



Unio is the principal genus, and contains the greatest num- 

 ber of species. It is known by having one or two short, robust 

 teeth at the hinge, and behind them one or two others, which 

 are flat and blade-shaped; the former are called cardinal — the 

 latter lamdlaf teeth. 



Alasmodon wants the lamellar teeth, and 



Anodon is without either kind. The following species in- 

 habit the Susquehanna and branches: 



Unio cariosus; shell straw yellow, 3 or 4 inches. U. radia- 

 tus; covered with broad green bands, 4 or 5 inches. U. com- 

 planatus ; compressed, dull brown, inside frequently purple ; 

 young sometimes rayed ; extremely variable in form ; our 

 most common species, 3 inches. U. viridis; a small, fragile, 

 brown or green, rayed species, with the cardinal teeth com- 

 pressed, and very variable ; usual length 1^ inch. 



Alasmodon undulatus; dark brown, rayed, a very robust 

 tooth in each valv«g, I5 inch. A. marginatus; green, rayed; 

 cardinal teeth small and thin ; posterior extremity of the shell 

 truncated ; 2 inches. 



Anodon cataractus; bright green, rayed; delicate, 4 or 5 

 inches. 



Anodon undulatus; dark brown, hinges slightly thickened, 

 having a tendency to form a slight pair of teeth, 2 or 3 inches. 

 See Conrad's work for information upon thisiiE^mily ; Binney's 

 on those of the land, and Haldeman's on the freshwater uni- 

 valve species. 



