226 MEMOIRS OF THE CARNEGIE MUSEUM. 



var. levigata. Farther up only the latter is found, but farther down the Ohio, 

 0. suhrotunda is common, and goes up into some of the tributaries (Little Kanawha 

 and Elk Rivers). The form from Elk River is peculiar, dwarfed, but with the 

 average diameter of sixty-one percent of the length."'' Sterki (1907fl) believes 

 that circulus {suhrotunda) is the male, and lens {levigata) the female. This is not 

 correct, for relying on Lea's figures, just the opposite would be true. On account 

 of this confusion it is not possible to trace the exact distribution of the two forms 

 in Ohio. 



In the rest of the range the two forms have not been kept strictlj^ separate. 

 It suffices here to say, that the range of the true suhrotunda covers, as Simpson 

 (1900) says: "the Ohio, Tennessee, and Cumberland river systems," that it does 

 not extend west of the Mississippi (Call, 1885), and that it is restricted to larger 

 rivers. This is substantiated by the material in the Carnegie Museum from 

 West Virginia, Kentucky, and Tennessee. Wilson & Clark (1914) report this 

 form from the upper Cumberland. 



0. suhrotunda has also been reported from the south in the Alabama and 

 Tombigbee drainages (Lea and Lewis, 1870), but this is questioned by Simpson. 

 A few specimens from this region in the Carnegie Museum resemble 0. suhrotunda 

 very much, but I have not enough material to decide the question. 



This species also crosses over into the lake-drainage in southern Michigan 

 and Ohio. Specimens from Lake Erie proper form a peculiar race (var. leihi), and 

 appear more closely related to suhrotunda, than to var. levigata. In the tributaries 

 of the lake (Maumee-drainage) the var. levigata is present. (See below.) 



0. suhrotunda in the Ohio prefers the shell-banks, in gravel and steady currents. 

 It is also found in small branches of the river, in the gi-avel of the riffles. 



Obovaria (Obovaria) subrotunda levigata (Rafinesque) (1820). 

 Obovaria lens (Lea) Simpson, 1914, p. 293; Ohovaria levigata (Rafinesque) Van- 

 atta, 1915, p. 552. 



Plate XIV, figs. 3, 4. 

 Records from Pennsylvania: 



Rhoads, 1899 (specimens from Beaver River, Wampum, Lawrence Co.). 

 Ortmann, 19096, p. 192 (included in circulus). 



Characters of the variety: Shell similar to that of typical suhrotunda, but more 



compressed, the diameter less than sixty percent of the length. Sometimes, but 



"■* But in Elk River also the diameter decreases in the upstream direction. At Sutton specimens 

 were found, which should be called var. levigata according to the diameter. 



