Hello All;
 
I've picked up some Corbicula during some recent walks along the Tennessee
River (yes, it's come to that, Unios are getting so scarce) and noticed there
seems to be two distinct varieties, differentiated by a consistent set of
characteristics.  Variety "2" is more inflated, thicker shelled, has a more
strongly projecting umbo, a more sharply curved posterior corner, and the
lateral teeth diverge at less than 90°, giving the shell a more strongly
triangular outline.  Variety "1" has the opposite features.  The relative
abundance of the two varies from place to place, but "1" is usually more
abundant.  Intermediate ones are not too common, and I did not see any with
mixed characteristics.
 
Also, many of the older corroded shells are much larger than the more recent
ones.  Does anyone have an opinion on these variations?
 
Thank you for your interest,
 
Martin Kohl