328 ORTMANN— THE ALLEGHENIAN DIVIDE. [April i8, 



investigated the number of species is not very great, and second, that 

 the natural affinities within this family are yet entirely obscure. 

 Nevertheless, some interesting points are easily observed, as will be 

 seen from the following account. 



A. The upper Ohio drainage in western Pennsylvania and 

 West Virginia has the following species : 



i. Pleurocera canaliculatum (Say) 



2. Pleurocera altipetum Anth. 



3. Goniobasis livescens (Mke.) 



(inch var. depygis (Say)) 



4. Goniobasis translucens Anth. 



5. Ancid osa dilatata (Conr.) 



It is to be remarked that the two Pleuroceras are restricted to the 

 larger rivers ; no. 1 is in the Ohio proper at and below Pittsburgh, 

 and has also been found as far up as the lower Youghiogheny in 

 Allegheny Co., Pa. ; while no. 2 is in the middle Allegheny up to 

 Venango and Warren Cos. No Pleuroceras have ever been found 

 in any of the smaller streams. 



Goniobasis livescens is in the Beaver drainage, and in that of 

 French Creek of the Allegheny (also in Lake Erie), and it appears 

 as if this species should be classed with those Najades which have 

 been mentioned (on p. 291, footnote 2) to be peculiar to those 

 drainages. The Goni ob as is- species of the Allegheny River, begin- 

 ning in the Ohio River below Pittsburgh, and going up through 

 Armstrong, Venango, Forest to Warren Co., is, according to Hink- 

 ley, G. translucens, and this species is also abundant in the drainages 

 of Beaver River and French Creek. 



Except in the lower Youghiogheny, where (many years ago) 

 Pleurocera canaliculatum has been found, no species of Pleurocera 

 or Goniobasis are known from the whole Monongahela drainage. 

 I have no doubt that some existed once at least in the lower Monon- 

 gahela, but the pollution of the waters apparently has exterminated 

 them, and no records have been preserved. The upper Yough- 

 iogheny, where the water is clear, is entirely without Pleuroceridce, 

 and this is positively established, for a search has been made for them. 



