UNIO. 
281 
/3. BatavL — Shell less thick than the preceding; 
the cardinal teeth oblique, less thick, some- 
times conic ; hinder teeth generally thick, ele- 
vated, but slightly elongate. 
7. RostratL — Hinge teeth generally thin and elon- 
gate ; the hinder side of the shell ending in an 
oblique more or less acute beak. 
I believe the first and last of these groups agree 
with the two British species, and that the presumed 
species are only varieties. 
