ALASMODONTA. 



GEKEKIC CHARACTER. 



Shell unattached, transverse equivalved, inequilateral : 

 cardinal teeth one in each valve, irregular, simple or bipar- 

 ted ; lateral teeth none ; muscular impressions two princi- 

 pal ones ; compound ligament exterior ; palleal line entire, 

 uniting the two muscular impressions. 



OBSERVATIONS. 



I formed this genus to receive several species of fluvia- 

 tile bivalves, which the characters of Unio and Anodonta 

 exclude. Lamarck placed some of the species in his 

 genus Unio, notwithstanding his character of lateral teeth 

 " allongee, comprimee, se prolongcant sous Ic corselet." 



Blainville in his "Manuel," has placed the genus as a sub- 

 genus under Anodonta, with Iridina of Lamarck and Dip- 

 sas of Leach. 



Cuvier in the first edition of his Regne Animal unites all 

 the genera of this family in Anodonta and Unioj and is still 

 followed in this arrangement by some other naturalists, 

 upon the principle that inosculating species destroy genera. 

 They appear to forget that the same principle would reduce 

 those two genera to a unit, and would in fact eliminate a 

 great portion of those groups, in all departments of Natu- 

 ral science. 



Four dilFerent names have been applied by as many 

 writers, to designate this genus. Leach called it Damar- 



K 



