Distribution of North American Viviparidw. 133 



The largest genus, Campeloma, will have the following 

 species and varieties : 



Campeloma ponderosum Say. 

 Campeloma decisum Say. 

 Campeloma subsolidum Anthony. 

 Campeloma integrum DeKay. 

 Campeloma, rufum Haldeman. 

 Campeloma coarctation Lea. 

 Campeloma decisum geniculum Conrad. 

 Campeloma limum Anthony. 

 Campeloma integrum obesum Lewis. 



The specific facts here indicated may not be in accordance 

 with those which are usually held by collectors. But this 

 arrangement is based upon the examination of several thousand 

 specimens from all over the wide range of territory to which 

 they belong. What disposition may be made of several prob- 

 lematical forms will depend upon more complete collections in 

 the southwestern portions of the Union. 



The species of Campeloma of widest geographic range is 

 Campeloma decisum Say. Hather more than two thousand 

 specimens of this form alone have passed in review during the 

 past twenty years until its particular features render it very 

 easy of identification. This form ranges from the Dartmouth 

 Lakes, Nova Scotia, northwestward through portions of Que- 

 bec and Ontario to the northern shore of Lake Superior and 

 on to the Saskatchawan river, British America. Throughout 

 all this region it is commonly scarce, being found nowhere in 

 abundance except in the St. Lawrence, near Montreal. From 

 Nova Scotia southwards the species ranges throughout New 

 England to Maryland and Virginia. It does not occur south 

 of the Ohio river in the region west of the Appalachian sys- 

 tem. That is to say no forms which may not better be re- 

 ferred to some other member of the group have yet occurred 

 south of that stream. The westernmost range of the form is 

 Michigan and Minnesota. Under the name of Campeloma 

 decisum however numerous shells belonging to the related 

 Campeloma subsolidum have been submitted to us and very 

 many more are to be noted in the United States National 

 Museum and in other large collections. But typical decisum 

 has to be looked for only within the portions of the country 

 above outlined. The variety herein designated as Campeloma 

 decisum geniculum Conrad will extend the range far to the 

 south but the characters of the variety appear to be so constant 

 and to have such well defined geographic limits that it is 

 deemed best to separately consider it. 



