I9I3.] ORTMANN— THE ALLEGHENIAN DIVIDE. 303 



*I2. Anodonta grandis Say 



*i3. Alasmidonta marginata (Say) 



*I4. Strophitus edentuhis (Say) 



15. Ptychohranchiis phaseolus (Hildr.) 

 *i6. Obovaria circulus lens (Lea) 

 *I7. Eurynia fabalis (Lea) 

 *i8. Eurynia iris (Lea) 

 *I9. Lampsilis luteola (Lam.) 

 *20. Lampsilis ovata ventricosa (Barn.) 

 *2i. Lampsilis multiradiata (Lea) 



22. Truncilla triquetra Raf. 



23. Truncilla perplexa rangiana (Lea) 



This is a fauna very similar to that farther below, but somewhat 

 depauperated. It is remarkable that this fauna goes far up, and 

 that there are yet 14 species at the uppermost locality (Weston), 

 where the river is merely a creek. Also here the rule holds good, 

 that the typical Ohio fauna decreases in richness in an upstream 

 direction, and that this decrease is gradual, not sudden. 



In sharp contrast to this are the eastern tributaries of the Monon- 

 gahela, which come down from the mountains. The first of them 

 is the Youghiogheny River. The fauna of the lower parts of this 

 river is entirely lost on account of pollution. Between Connelsville 

 and Confluence, Fayette Co., Pa., the river runs through a canyon, 

 is very rough, forming falls (largest at Ohiopyle). Above Con- 

 fluence it is less rapid, and flows in a broad valley, offering condi- 

 tions favorable to Najades ; but only a single species is found here : 

 Strophitus edentulus (Say). 



The next of the mountain streams is Cheat River. Also this 

 river runs through a long canyon, and above this canyon there are 

 no Najades in it.^ But below the canyon the fauna is rich. In the 

 following list, the species marked * are found also at Mont Chateau, 



* I collected above Parsons, Tucker Co., W. Va., in Shavers Fork. Below 

 Parsons the river is badly polluted, and also Dry Fork is polluted through 

 Blackwater River. I have been told that there used to be some shells in the 

 Cheat, below Parsons, but we have no means of ascertaining what species 

 they were. 



PROC. AMER. PHIL. SOC, LII, 210 B. PRINTED JULY II, I913. 



