210 



MEMOIRS OF THE CARNEGIE MUSEUM. 



usual, and thus there is in the mountains a tendency toward the formation of a 

 small race. Lake Erie possesses a somewhat peculiar form (Plate XIII, fig. 3), 

 in which the specimens remain small; the dimensions of the largest at hand, a 

 gravid female, being: L. 72, H. 40, D. ^4 mm., and they assume the humped shape 

 when comparatively small. Further, the growth-lines are more crowded, and 

 more regular, but not very distinct (not marked by color). Young shells of the 



Fig. 22. 



■ ElUpsaria fasciolaris. 



• Obliquaria reflexa. 

 + Cyprogenia stegaria. 

 X Do. (Indian garbage heap). 



form from Lake Erie are indistinguishable from specimens of the same size from 

 the Ohio-drainage. I do not think it advisable to distinguish the lake-form by a 

 varietal name, but the tendency to develope a local race is clearly indicated in 

 this case. 



Specimens from Conneaut Creek (tributary to Lake Erie) are entirely normal. 



It should be mentioned that the form from Chautauqua Lake in New York 

 inclines toward that of Lake Erie in the more crowded growth-lines, and the average 

 size, a fact which is apparently due to the parallel influence of the environment. 



Localities in Pennsylvania, represented in the Carnegie Museum: 



Small tributaries of Ohio: 



Little Beaver Creek, Cannelton (Miss Vera White & H. H. Smitli) and New Galilee, Beaver Co.; Enon 



Valley, Lawrence Co. 

 Raccoon Creek, New Sheffield, Beaver Co. 



