332 ORTMANN— THE ALLEGHENIAN DIVIDE. [April 1 8, 



of the divide. The present case most resembles that of Symphynota 

 tappaniana, where we have a species found both in New River and 

 on the Atlantic side. The range of the latter is not entirely identical, 

 for it is not found in the Monongahela drainage, and goes, on the 

 Atlantic side, farther north, while A. carinata only reaches the Sus- 

 quehanna in which it goes up to New York state. 



III. FAMILY: VIVIPARID^; GENUS: CAMPELOMA RAF. 



Also in this group we lack a modern revision of the species, and 

 there is much uncertainty with regard to the geographical distribu- 

 tion. What I have collected in Pennsylvania, West Virginia and 

 Virginia apparently falls under three described species : Campeloma 

 decisum (Say), C. ruf urn (Hald.), and C. ponder o sum (Say), and 

 with the first one I unite as undistinguishable, what has been called 

 C. integrum (Say). At any rate, I am not able to distinguish the 

 common form of the upper Ohio drainage in western Pennsylvania 

 and West Virginia from the common form of the Atlantic side 

 (from Delaware to James). The identical form is also in Clinch 

 River. 



C. decisum seems to prefer the larger rivers, but it is not absent 

 in the headwaters, and I have it from the mountain region on either 

 side of the divide (Shaver's Fork, upper Tygart system, Greenbrier, 

 uppermost tributaries of Allegheny, and many places in the head- 

 waters of the Potomac and James). Consequently, this would be 

 again a case where an identical species is found on either side of the 

 divide, and where this divide does not form a barrier to the dis- 

 tribution. 



Of the other two species, C. rufum is known to me only from 

 northwestern Pennsylvania, in the Allegheny and its tributaries 

 (French Creek) and in the Beaver and Little Beaver drainage. This 

 looks very much as if it belonged to those forms, which invaded 

 Pennsylvania from the west, coming " across country." (After all, 

 this may be only a local form of C. decisum, with which it is often 

 found associated.) 



I found C. ponderosum only in Elk Creek, West Virginia, and 

 farther down in the Ohio (Portsmouth, Scioto Co., Ohio). Here it 



