UPPER TENNESSEE DRAINAGE. 537 



associated with bigbyensis. Farther down, barnesiana soon begins 

 to prevail. The form bigbyensis has been traced down in the Powell 

 to Combs, Claiborne Co., Tenn. ; in the Clinch to Clinchport, Scott 

 Co., Va. ; but a single specimen has been found at Solway, Knox Co., 

 Tenn., apparently an exceptional case ; in the Holston it has not been 

 found below the point where the North and South Fork unite. 



Type locality: Big Bigby Creek, Maury Co., Tenn. (trib. to Duck 

 River and lower Tennessee). 



II. FuSCONx-MA BARNESIANA TUMESCENS (Lea), 1845. 



Unio tumescens Lea, '^$.—Unio crudus Lea, '71. — Unio radiosus 

 Lea, '71. — Unio tumescens Lewis, '72. — Unio tumescens Pilsbry 

 & Rhoads, '96. — Pleurobema tumescens and P. crudiim Simpson, 

 '14, p. 751, 753. — Fiisconaia barnesiana tumescens Ortmann, '17, 



P- 59- 



(Simpson makes radiosus a synonym of tumescens.) 



This is the swollen form of the large rivers, with a diameter of 

 50 per cent, of the length, and over. It also generally has higher 

 beaks, making the outline of the shell more nearly triangular; but 

 higher beaks are also sometimes observed in the typical F. barnesiana 

 (lyoni-type) . U. tumescens represents the extreme in obesity, and 

 radiosus (type examined!) is very close to it. U. crudus is the much 

 eroded form of the French Broad River (topotypes at hand). The 

 two former have more or less developed rays, the latter is rayless. 



F. barnesiana tumescens has its metropolis in the Tennessee 

 River at and below Knoxville. But it is also found some distance 

 in the rivers above this point. From the Clinch it is known from the 

 lower part ; the uppermost locahty is at Edgemoor, Anderson Co. It 

 also has been reported (by Pilsbry and Rhoads) from Emory River 

 at Harriman, Roane Co. In the Holston proper I have observed it 

 as far up as Noeton, Grainger Co. It is also in the lower French 

 Broad, at Boyd Creek, Sevier Co., in the Little Tennessee in Monroe 

 Co., and in Hiwassee River, at Austral, Polk Co. (intergrading, at 

 these places, with typical F. barnesiana) . 



Remarkably enough, a small tributary of Little River, Pistol 

 Creek, Rockford, Blount Co., Tenn., contains shells, most of which, 



PROC. AMER. PHIL. SOC, VOL. LVII, JJ, SEPT, 30, I918. 



