Mr. Barnes on the Genera Unio and Alasmodonta. 275 



Inhabits the Fox River. Mr. Schoolcraft. 



Cabinet of the Lyceum. 



Mr. Colhns's Collection. 



Mr. Say's Collection, Philadelphia. 



Diam. -35—525 Length -4— -6 Breadth -75— 1-2. 



Shell rather thin, beaks placed about one fourth of the 

 length from the posterior extremity, ligament very narrow, 

 anterior lunule distinct and obsoletely ribbed ; basal margin 

 slightly shortened ; epidermis brownish ; an obtuse slight- 

 ly elevated rib from the beaks to the anterior basal marginj 

 lateral tooth rectilinear rounded at the end, and parallel to 

 the base ; naker very brilliant. 



Remark. — The smallest and most beautiful of all the 

 genus yet discovered in America. 



Summary of the Unio. 



Species described, ----- 28 



Varieties particularized, - - - - 23 



Total of species and varieties, - - - 51 



Of \\hich Mr. Say formerly described, - 8 



We have given new specific names to - 20 



Of which M. Lamarck had jJerAops previously no- 

 ticed .------3 



End of the Unio. 



ALASMODONTA.* 



Generick Character. 



Shell transverse, equivalve, inequilateral, free; beaks 

 decorticated; posterior muscular impression compound; 

 hinge with prominent cardinal teeth in each valve, but 



ioithout lateral teeth. 



* " From*, without, \ii<r/ux (^trirjux ?) a scale, andt/ofc a tooth."— Jtfr. Say, 



