Ort.mann : Unionid.e of Western Pennsylvania. 203 



13. Unio gibbosus Barnes. 

 Presque Isle Bay. 



The lake form of this species is rather peculiar, being small and of 

 lighter color than the typical form from the Ohio drainage. 



14. Quadrula undulata hippopaea (Lea). 

 Presque Isle Bay. 



This peculiar variety by no means belongs to Q. plicata under 

 which it is placed by Simpson. It is clearly a descendant of Q. undu- 

 lata of the Ohio drainage, and distinguished by its smaller size, and 

 slightly more elongated form. The development of the undulations 

 does not differ at all from the typical form, or rather, both forms show 

 the same variations. There are many specimens of Q. undtilata in the 

 Ohio drainage, chiefly young ones, which come very close to the var. 

 hippopcea. 



15. Quadrula rubiginosa (Lea). 



Horseshoe Pond on Presque Isle and Presque Isle Bay. 



Not at all typical, but of small size, and rather swollen shape, thus 

 closely approaching Q. trigoua ; in fact . I have a specimen, which 

 might safely be called trigona. 



16. Quadrula coccinea (Conrad). 



Not found in the lake, but in Conneaut Creek. I obtained a single 

 dead shell, agreeing with the normal form of the Ohio drainage of 

 northwestern Pennsylvania. 



17. Quadrula subrotunda (Lea). 

 Presque Isle Bay. 



A peculiar dwarfed form. 



C. Atlantic Drainage. 



The species of the Atlantic drainage in Pennsylvania are rather well 

 known, yet our knowledge of them is restricted mainly to the south- 

 eastern section of the state. The distribution of the single forms has 

 never been investigated in detail, and we do not know how far they 

 go up in the rivers. It seems that some species are rather generally 

 distributed, while others are more or less restricted, either to the lower 

 parts of the rivers, or to one river drainage only. The following list 

 is intended to collect the known facts of distribution, adding new 

 locality-records, which are represented by specimens in the Carnegie 

 Museum. The older records are compiled from the following papers : 



Gabb, A. F. " List of MoUusks inhabiting the neighborhood of 

 Philadelphia." (Proc. Acad. Philadelphia, 1861, p. 306.) 



