528 ORTMANN— NAYADES OF 



of the latter. I have seen the normal suhrotnnda 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 Hne 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), 184O. 



Unio lesueurianus Lea, '40. — Quadrula flexuosa Simpson, '00. — 

 Quadriila flexuosa Simpson, '14, p. 887. 



According to Simpson, '14, p. 894, lesueuriana is synonym to 

 pilaris. 



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 flexuosa, and 

 thus labeled by Marsh. Two of these, with the diameter of 53 and 

 54 per cent., are lesueuriana, while one (Knoxville), with diameter 

 of 56 per cent., is pilaris. Simpson's measurements of flexuosa give 

 the diameter of 51 per cent., and thus it should be made a synonym 

 of lesueuriana. 



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 



