322 ORTMANN— THE ALLEGHENIAN DIVIDE. [April i8, 



Lampsilis ovata cohongoronta Ortm. has been dropped as not 

 indigenous on the Atlantic slope. 



The following facts are observed : 



1. Probably seven species of these have a rather general distri- 

 bution. In five of them this is perfectly clear (nos. 3, 8, 12, 14, 16), 

 but probably also nos. 7 and 11 fall under these; they only may 

 have been overlooked in certain regions. 



2. There are six forms, which apparently have a more northern 

 range, disappearing toward the south, nos. 1, 9, 18, 19, 20, 21. The 

 last four have the peculiarity in common that toward the south they 

 become more or less restricted to the coastal plain. 



3. On the other hand, there are six forms, which have their 

 center more toward the south and disappear toward the north. 

 These are the nos. 2, 4, 5, 6, 10, and 17. 



4. Of the two remaining forms, no. 13 is a local form of the 

 Susquehanna drainage, while no. 15 is altogether doubtful, but may 

 be a local (tidewater) form of no. 16. 



Compared with the western fauna of 47 species (list no. 1), the 

 Atlantic fauna is decidedly poor (less than half the number of spe- 

 cies). But in the Ohio we notice a general and marked decrease of 

 species in the headwaters, so that there are only fourteen species 

 in the headwaters of the Allegheny River. In the eastern drainage 

 systems, there is also a slight decrease toward the headwater, but 

 this is much less in proportion, and in the mountain region we have 

 yet thirteen species (nos. 1, 2, 3, 5, 7, 8, 10, 11, 12, 13, 14, 16, 17). 

 Thus we may say, that, disregarding a few species restricted to the 

 lowlands and the larger rivers, the fauna of the Atlantic streams 

 remains, in each river system, rather uniform up to the headwaters, 

 decreasing hardly in the number of species. 



Further, in the region of the headwaters of the Monongahela 

 and Kanawha, the conditions are actually reversed. Here only very 

 few species (not more than three) are found in the western streams, 

 while the eastern streams (Potomac, James) have decidedly more, 

 the James, for instance, at least eight, possibly ten. Thus the At- 

 lantic fauna is here richer than the western. 



But the Tennessee fauna (list no. 16) again holds its own, and 

 the Atlantic fauna falls by far short of it. 



