I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 315 



Margaritana margaritifera, and still exists there, and I have col- 

 lected it repeatedly in 1909 and 1910. But it has become very rare, 

 and is restricted to some small, clear, and cold mountain runs, in 

 which no other Najades are found. This species stands by itself, 

 and, as we shall see below, needs special discussion. 



II. The Fauna of the Susquehanna River. 



The following is a list of the species, positively known to occur 

 in the Susquehanna drainage : 5 



List No. 18. 



1. Elliptio complanatus (Dillw.) 



2. Symphynota tappaniana (Lea) 



3. Anodonta Cataracta Say 



4. Alasmidonta undulata (Say) 



5. Alasmidonta marginata susquehannae Ortm. 



6. Alasmidonta varicosa (Lam.) 



7. Strophitus edentulus (Say) 



8. Lampsilis radiata (Gmel.) 



9. Lampsilis cariosd (Say) 



The lower Susquehanna, in Maryland, is unknown. Possibly, 

 the lowland and tidewater species, Elliptio fisherianus and Lamp- 

 silis ochracea, might be found there. And further, Alasmidonta 

 heterodon has not been taken in the Susquehanna drainage, although 

 it is present to the north and south of it. Even adding these three 

 species, the fauna of the Susquehanna falls short of that of the 

 Delaware by three species; four seem to be absent {Margaritana 

 margaritifera, Anodonta implicata, Strophitus undulatus, Eurynia 

 nasuta), while Alasmidonta marginata susquehannae is added. The 

 first two species surely reach their southern boundary in the Dela- 

 ware drainage, while the doubtful Strophitus undulatus seems to be 



6 Anodontoides ferussacianus (Lea) has been reported from the head- 

 waters of the Susquehanna in New York state. It is not found in Pennsyl- 

 vania, and the New York record should be confirmed ; but even when correct, 

 this may be neglected, for this species surely does not belong to the original 

 fauna of this system, but is a postglacial immigrant. 



