330 ORTMANN— THE ALLEGHENIAN DIVIDE. [April 18, 



is the only genus found, and it is represented in all these streams by 

 one and the same species, A. dilatata. This genus is not found any- 

 where else in the whole upper Ohio drainage in West Virginia and 

 Pennsylvania, but it is represented on the Atlantic side by a closely 

 allied and widely distributed species. It is perfectly clear that this 

 case does not submit to the same laws which governed the Najad 

 fauna and the other Pleuroceridce of this region. Further particu- 

 lars will be given below. 



As regards the upper Tennessee fauna (Clinch and Holston 

 rivers), we have here again a rich development of Pleuroceridce, as 

 is well known. I do not think that my collections represent this 

 fauna fully, but I have collected the following species : 



i. Io fluvialis (Say) (Holston and Clinch) 



2. Pleurocera estabrooki (Lea) (Holston) 



3. Pleurocera knoxense (Lea) (Holston) 



4. Pleurocera unciale Hald. (Clinch, also, as we have 



seen, in Big Sandy.) 



5. Goniobasis simplex (Say) (Holston and Clinch) 



6. Anculosa gibbosa Lea (Holston and Clinch) 



Io is a type entirely peculiar to this region. Except PL unciale, 

 which is also in the Big Sandy, the others have no striking relation- 

 ship to any of the species mentioned above from the upper Ohio. 

 The Anculosa may have a somewhat closer genetic relationship with 

 the Anculosas farther north, in New River, etc., but morphologically 

 they are distinctly separated. 



Thus it is clear that the Pleurocerid- fauna of the upper Ten-, 

 nessee undoubtedly corresponds to the Naj ad-fauna of this region, 

 and probably has had a similar history. 



B. Pleuroceridce of the Atlantic Side. 



The genus Pleurocera is entirely missing on the Atlantic side. 

 Goniobasis is represented by two species: 7 G. virginica (Gmel.) and 



7 Additional species are found from North Carolina southward. G. nick- 

 liniana Lea has been reported (Tryon, '66, p. 31) from Bath Co., Va. (orig- 

 inal locality: near Hot Springs, drainage of Jackson River). This species is 

 unknown to me. I collected in Jackson River at Covington, Alleghany Co., 



