I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 317 



species in this uppermost part of the drainage of West Branch. 

 Alasmidonta marginata susqtiehannae has not been found here. 



The seven species of the upper Susquehanna drainage are the 

 same as those of the Delaware, with the exceptions that in the 

 former Margaritana and Alasmidonta heterodon are missing, while 

 in their place Symphynota tappaniana and Alasmidonta marginata 

 susqiiehannae turn up. Thus there are five species common to both 

 drainages. 



Further investigations may change this slightly. But this seems 

 to be assured, that although similar faunas exist in both rivers, the 

 Susquehanna falls short by several species of the Delaware, and 

 that the lack is made good only in part by the presence of a local 

 form, Alasmidonta marginata susqiiehannae. 



III. The Fauna of the Potomac River. 



The following species are positively known to exist in the 

 Potomac drainage : 



List No. ip. 



1. Elliptio complanatns (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) 



8. Lampsilis radiata (Gmel.) 



9. Lampsilis ovata cohongoronta Ortm. 



10. Lampsilis cariosa (Say) 



11. Lampsilis ochracea (Say) 



In addition, there might be, in the lower Potomac, Elliptio fish- 

 erianus (Lea) and Eurynia nasuta (Say) ; these have been frequently 

 confounded, but forms like them are positively known to occur in 

 the Potomac at Washington. Possibly both of them are there. 

 Further, there might be, in the tributaries on the Piedmont Plateau, 

 Alasmidonta heterodon (Lea), which is found both to the north and 

 south of the Potomac drainage. 



