203 ANNALS OF THE CARNEGIE MUSEUM. 
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 hippopea (Lea). 
Presque Isle Bay. 
This peculiar variety by no means belongs to Q. flcatfa under 
which it is placed by Simpson. It is clearly a descendant of Q. wndu- 
fata 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. wadu/afa in the 
Ohio drainage, chiefly young ones, which come very close to the var. 
hippopea. 
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. ¢77gona; in fact I have a specimen, which 
might safely be called “vzgona. 
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 Mollusks inhabiting the neighborhood of 
Philadelphia.’’ (Proc. Acad. Philadelphia, 1861, p. 306.) 
