118 



MEMOIRS OF THE CARNEGIE MUSEUM. 



angle. The degree of compression is also variable; some specimens being more 

 swollen in the region of the posterior ridge than others. Furthermore, some speci- 

 mens are more elongated than others, but all these arc individual variations, and I 

 never have noticed any distinct tendency to form local races. 



Specimens from Conneaut Creek (Erie-drainage) do not differ from the normal 

 form of the Ohio-drainage. Specimens from the headwaters of the Genesee River 

 are identical with the type. The only two specimens I collected from Lake Erie 

 were not from the lake proper, but from beach-pools, cut off from the lake by 



Fig. 12. 



■ Lasmigona viridis. 



• Lasmigona complanata. 

 + Lasmigona costata. 

 X Lasmigona costata eriganensis. 



sand-bars. They are entirely normal, but have a peculiar rusty brown tint in the 

 epidermis, such as is found in other Naiades from Lake Erie, and especially in 

 specimens from the beach-pools. A third individual from the lake, from Cedar 

 Point, Ohio, is also normal in color. 



Localities in Pennsylvania represented in the Carnegie Museum: 



Little Beaver Creek, Canneltou (Miss Vera AVhite) (H. H. Smith), Darlington and New Galilee, Beaver 



Co.; Enon Valley, Lawrence Co. 



Beaver-drainage: 

 Beaver River, Wampum, Lawrence Co. (G. H. Clapp & H. H. Smith). 

 Brush Creek, Celia, Beaver Co. 

 Mahoning River, Mahoningtown, Lawrence Co. 

 Neshannock Creek, Eastbrook, Lawrence Co. 



