84 MEMOIRS OF THE CARNEGIE MUSEUM. 



the difference in this respect is not great. There is much variation in shape, 

 chiefly with regard to the elongation of the shell and the position of the beaks. 

 In some specimens the beaks are much anterior, thus imitating the condition seen 

 in P. obliquum rubrum. 



The color of the epidermis is generally dark brown, but specimens from Michi- 

 gan are light brown, with greenish capillar}^ rays; however, these specimens are 

 greatly water- worn. 



I have not seen any specimens grading toward the parent-form, and for this 

 reason, we might perhaps be justified in regarding this as a true species. Never- 

 theless I hesitate to take this course, since I consider my material (about fifteen 

 specimens) as insufficient to settle this question. 



Localities represented in the Carnegie Museum: 



Lake Erie, Prcsciue Isle Bay, Erie, Erie Co., Pennsylvania. 



Lake Erie, La Plaisance Bay, Monroe Co., Michigan (C. Goodrich). 



Distribution and Ecology (See fig. 8): Type locality, St. Lawrence basin at 

 Niagara Falls (Simpson). 



Sterki mentions this form, as a dwarf race of Q. subrotunda, from the Ohio 

 shores of Lake Erie. Walker gives it (1913, p. 29) from Lake Erie, and probably 

 his Q. subrotunda refers to the same form. I have found it in Presque Isle Ba}^ 

 and received specimens from La Plaisance Bay. Probably, Marshall's (1895) 

 U, coccineus from Erie Co., New York, is also this. 



Our present knowledge thus limits its range to Lake Erie and the Niagara 

 River just below it. Simpson, indeed, says "and tributaries," but exact localities 

 are not given. 



In Presque Isle Bay I found this shell only on the North shore in a few feet 

 of water upon pure sand, but most of my specimens were dead shells. It is decidedly 

 rare at this locality. 



Pleurobema obliquum rubrum (Rafinesque) (1820). 

 Quadrula pyramidata (Lea) Simpson, 1914, p. 888; Quadrula rubra (Rafinesque) 

 Vanatta, 1915, p. 557. 



Plate VI, fig. 7. 

 Records from Pennsylvania : 



Harn, 1891 (as mytiloides) (western Pennsylvania). 

 Stupakoff, 1894 (Allegheny Co.). 

 Ortmann, 19096, p. 199 (under ohliqua). 



Characters of variety: Like P. obliquum, but shell very oblique, with the beaks 



