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 swbrotunda (diameter 60 per cent. and over). A fourth 
specimen, found associated with these has the diameter of 55 per 
cent., and should be called O. 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 levigata Rafinesque, ’20.—Obovaria (Obovaria) lens Simpson, 
"14, p. 293.—Obovaria levigata Vanatta, ’15, p. 552. 
Already Conrad (1834) has seen that Jevigata 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 abundant 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. 
