300 



MEMOIRS OF THE CARNEGIE MUSEUM. 



observations, it inhabits in these the roughest parts, riffles with strong currents, 

 the bottoms consisting of large stones, loosely piled over each other, with little 

 finer material packing them together. Of course, occasionally it is found also in 

 finer gravel. I have no doubt, that its chief characters are reactions to the con- 

 ditions prevailing in riffles. The flattened or concave, truncate posterior slope is 



Fig. 32. 



• Lampsilis ovata. O Indian garbage heap. 



■ Lampsilis ovata ventricosa. 



+ Lampsilis ovata canadensis. 



produced by the current and the material rolled by it over the posterior end of the 

 shell, when it is imbedded in the gravel; and the wedge-like attenuation of the 

 anterior end is a device to enable the shell to plough through the heavy gravel in 

 which it lives. I have seen the shell moving along in coarse gravel, and pushing 

 aside stones, which were much larger than itself. 



General distribution: Type locality, Ohio (Say). 



It seems that the Ohio River, the Cumberland, and the Tennessee represent 

 the metropolis of this species. Aside from western Pennsylvania, it is found in 

 the Ohio proper in West Virginia (Carnegie Museum), Ohio (Sterki, 1907a), 

 Indiana (Call, 1896a and 1900), and Illinois (Baker, 1906). It occurs in very few 

 of the tributaries. Hildreth (1828) gives it from the Muskingum River at Marietta, 

 Washington Co., Ohio; Sterki (1907a) from the Great Miami River; and Call 

 from the Wabash, White, and Eel Rivers. In addition, I have found it in Elk 

 River in West Virginia, but only as far up as Clay County. Above this point, 

 its place is taken by ventricosa, and the mutual relations of these two forms are 



