XXXVll 



4. Shell hea\y, oval, truncate, oblong, or turreted ; aper- 

 ture entire above. — [Figs. 12, 13.] GoNiOBAsis,Lea. 



5. Aperture with a sutural, pleurotomose slit above. — 

 [Fig. 14.] Mp:sesch izA,Lea. 



6. Lip slit in the middle. — [Fig. 15.] Schizostoma, Lea. 



III. Aperture entire and rounded in front. 



7. Shell oval, heavy ; columella callously thickened 

 above. — [Fig. 16.] Anculosa, Say. 



Fig. 12. Fig. 13. Fig. U. Fig. 15. Fig. IG. 



2. Geograpkical Distribution. — We have, in North 

 America, nearly five hmidred recognized species 

 of the shells belonging to the various genera of 

 Str€2)omatidce. So considerable a moiety of these 

 are found to be inhabitants of the upper Tennessee 

 River and its branches in East Tennessee and North 

 Alabama, and of the Coosa River in the latter State, 

 that we quite agree with Mr. Lea in regarding that 

 region as the great centre of this kind of animal 

 life. We have ascertained that, leaving out the 

 .species inhabiting the Pacific States and those which 

 in the descriptions have their habitats designated 

 by States only,* of the remainder, fully two-thh'ds 

 belong to the above two streams; including three 

 entire genera, nearly all the species in several others, 

 and a majority of the species of every genus except 

 one (Meseschiza) of a single species. 



The Strepomatidce do not appear to flourish in the 

 neighborhood of the sea, and nowhere have the 



* As the localities of nearly all of these are "Tennessee" or 

 "Alabama," the most of them also were probably obtaiut;d from the 

 Tcuuessee aud Coosa Rivers. 



