528 ORTMANN—NAYADES OF 
of the latter. I have seen the normal subrotunda from the Tennessee 
in northern Alabama, but I cannot tell whether the two pass into 
each other. 
The typical form of F. pilaris passes into the following local 
races in an upstream direction, and it is hard to draw a line between 
them. In order to preserve the oldest names given, I have arbitrarily 
concluded to call by this name those more swollen forms where the 
transverse diameter of the shell is 55 per cent. of the length and over. 
This typical F. pilaris is restricted to the large rivers: Tennessee, 
lower part of Little Tennessee, lower French Broad, lower Holston 
and lower Clinch. In the two latter rivers it is rare, and intergrades 
with the next form, going up, in the Holston, to Grainger Co., and, 
in the Clinch, to Anderson Co., Tenn. 
Type locality: French Broad River, Tenn., and Holston River, 
Tenn. (topotypes examined). 
3. FUSCONAIA PILARIS LESUEURIANA (Lea), 1840. 
Umo lesueurianus Lea, ’40.—Quadrula flexuosa Simpson, ’00.— 
Quadrula flexuosa Simpson, ’14, p. 887. 
According to Simpson, ’14, p. 894, lesweuriana is synonym to 
pilarts. 
Like pilaris, but less swollen; the diameter of the shell is from 
45 per cent. to 54 per cent. of the length. 
Of Q. flexuosa, I have seen, in the Walker collection, two speci- 
mens from Holston River, Knoxville (Mrs. Andrews), and one 
specimen from Holston River, Hamblen Co. (opposite Grainger Co.) 
(Marsh). They had been compared with the type of flerwosa, and 
thus labeled by Marsh. Two of these, with the diameter of 53 and 
54 per cent., are lesweuriana, while one (Knoxville), with diameter 
of 56 per cent., is pilaris. Simpson’s measurements of flerwosa give 
the diameter of 51 per cent., and thus it should be made a synonym 
of lesweuriana. 
This is the form of the medium rivers; it turns up in single indi- 
viduals in the region of Knoxville, and becomes the prevailing form 
in the lower Clinch and in the whole Holston proper. In the Clinch, 
it has been traced up, in single individuals, to Scott Co., Va., and it 
