11 
small streams. Rafinesgiue observes of the U.Jiavus , 
that it is “found only in the small rivers falling into 
the Kentucky, Salt or Green rivers . 57 It occurs, 
however, in Alabama, where it observes the same 
peculiarity in the choice of its habitat. Other 
species prefer the soft muddy shores to the bars, 
which are the usual localities of the Naiades; amongst 
these are ZJnio teres , Raf. ( U. anodontoides , Lea,) 
and U. cariosus ? Say: U.fragilis , Raf. ( U. gracilis, 
Barnes, Symphynota gracilis , Lea,) is abundant on 
the rocky shores of the Alabama river, at Claiborne, 
as well as on many of the bars. 
The limited range of some fresh water shells, and 
the wide distribution of others is very remarkable. 
A large Paludina adheres to the rocks in the vicinity 
of Claiborne in vast numbers, yet I have not else- 
where observed it, not even at St. Stephens, on the 
Tombeckbe, where fragments of the rocky strata 
strew the margin of the river in the same manner as 
at Claiborne, and such calcareous masses appear to 
be the only resort of the species. In like manner the 
*Fusus Jluvialis of Say appears to be limited to the 
* lofusiformis , Lea. It was improper to change the 
specific name of this shell, for good or bad specific names 
it is generally conceded, must stand, unless they are pre- 
occupied in the same genus. The animal of this shell is 
