568 ORTMANN— NAYADES OF 



and Pilsbry & Rhoads). I know it only from the Holston River at 

 Mascot, Knox Co., where I found three specimens with the diameter 

 of 60, 61 and 62 per cent, of the length. These must be placed with 

 typical subrotunda (diameter 60 per cent, and over). A fourth 

 specimen, found associated with these has the diameter of 55 per 

 cent., and should be called 0. subrotunda levigata (which see). 



In this region, there is evidently no tendency of this form to go 

 into the small streams of the headwaters, although my specimens 

 from the Holston indicate an inclination toward the small stream 

 form levigata. 



Type locality: Ohio River (type from Kentucky River, accord- 

 ing to Vanatta). 



53. Obovaria (Obovaria) subrotunda levigata 

 (Rafinesque), 1820. 



Unio /^z/j^'afa Rafinesque, '20. — Obovaria (Obovaria) Icus Simpson, 

 '14, p. 293. — Obovaria levigata Vanatta, '15, p. 552. 



Already Conrad (1834) has seen that levigata Raf. is the same as 

 lens Lea. 



This is the small stream form of the main species, distinguished 

 by greater compression of the shell (diameter less than 60 per cent, 

 of the length). It is quite a'bundant in the tributaries of the Ten- 

 nessee below the Walden Gorge (Sequatchie River, Tenn., Flint 

 River and Hurricane Creek, Madison Co., Ala., Elk River and Bear 

 Creek). It intergrades here with the main species, as it does in the 

 upper Ohio region. 



From above the Walden Gorge, I have it from South Chicka- 

 mauga Creek, Ringgold, Catoosa Co., Ga. From the headwaters 

 region, above Knoxville, I have just two specimens from the Hol- 

 ston, one from Mascot, another from Holston Station, Grainger Co., 

 in which the diameter falls under 60 per cent, (to 55 per cent, in the 

 first, to 57 per cent, in the other). I have never seen a trace of this 

 form in the small streams of this region. 



Type locality: Kentucky River. 



