318 ORTMANN— THE ALLEGHENIAN DIVIDE. [April i8, 



No. 9, Lampsilis ovata cohongoronta, should be disregarded, and 

 dropped from the list of the original fauna of the Potomac, for it 

 probably is a modern introduction from the west (Ortmann, 1912&). 



Thus, including the doubtful forms, there would be 13 species 

 belonging to the Potomac drainage. This is two less than in the 

 Delaware; while three of the latter are missing here (Margaritana 

 margaritifera, Anodonta implicata, Strophitus undiilatiis) , one other 

 is added, Elliptio productus. This latter case is important, because 

 we positively know that this species is a southern form, which 

 reaches its most northern range in the Potomac. 



Aside from Elliptio fisherianus and Eurynia nasuta, which, when 

 present, are found only in the lower Potomac, three others, Lamp- 

 silis radiata, cariosa, and ochracea, are restricted to the lower parts 

 of the drainage, below the gap in the Blue Ridge at Harper's Ferry. 

 Above and to the west of this point, that is to say, in the Allegheny 

 Valley and the Allegheny Mountains, only the following species are 

 present (of course, disregarding the introduced no. 9) : 



1. Elliptio complanatus (Dillw.) 



2. Elliptio productus (Conr.) 



3. Symphynota tappaniana (Lea) 



4. Anodonta cataracta Say 



5. Alasmidonta undulata (Say) 



6. Alasmidonta varicosa (Lam.) 



7. Strophitus edentulus (Say) 



Also here, seven species ascend into the headwaters, and among 

 them there are again the same five {Elliptio complanatus, Anodonta 

 cataracta, Alasmidonta undulata, Alasmidonta varicosa, Strophitus 

 edentulus) which we have seen to be common to the headwaters of 

 the Delaware and Susquehanna. An additional one, Symphynota 

 tappaniana, is also found in the Susquehanna, while Elliptio pro- 

 ductus is a new element in this fauna. 



I do not think it necessary to give further particulars. But 

 again it should be noted, that the distribution of these species is 

 rather erratic, and that they generally are not all found associated. 

 Elliptio productus has not been found yet in the region of the Alle- 



