UPPER TENNESSEE DRAINAGE. 545 



cypliyus often has these knobs nearly obliterated. Whether the soft 

 parts are always pale remains to be seen (the specimen of typical 

 cypJiyiis from the same locality had orange soft parts) : but several 

 other shells have, in the French Broad, the tendency to develop pale 

 soft parts, or pale nacre, while they are tinted elsewhere. 



This seems to be a rare shell, which has been reported by Lewis 

 from the Tennessee below Knoxville, by Frierson from the " Clinch 

 and Holston " ; Walker has specimens from " Holston, Knoxville " 

 (probably Tennessee), and I found it in the lower French Broad. 

 It might be that this is a local race, restricted in its distribution, and 

 possibly with its center in the lower French Broad : but more mate- 

 rial with exact localities should be secured. 



Type locality: Clinch and Holston rivers. 



Genus: Lexingtonia Ortmann (1914). 

 Ortmann, 1914, p. 28. 



23. Lexingtonia dolabelloides (Lea), 1840. 



Uiiio dolabelloides Lea, '40. — Unio thorntoni Lea, '57. — Unio moore- 

 sianiis Lea, '57. — Unio recurvatus Lea, '71. — Unio circumactus 

 Lea, '71. — Unio subglobatns Lea, '71. — Unio dolabelloides and 

 mooresianns Lewis, '71. — Pleurobenia dolabelloides Simpson, '14, 

 P- 752. 



U. thorntoni, mooresianns, recurvatus, circumactus, and subglo- 

 batus have been recognized by Simpson as synonyms of this. 



Also here we have a case where a swollen form {dolabelloides) 

 is found in the larger rivers, and a compressed one (coiiradi) in the 

 smaller streams, with the intergrades existing between them. I have 

 drawn the line between the two at the diameter of 50 per cent, of 

 the length, so that forms with the diameter 50 per cent, or over are 

 dolabelloides, and those below 50 per cent, are conradi. 



L. dolabelloides in its typical development is a swollen form, gen- 

 erally also with more elevated beaks. It is known from the Ten- 

 nessee River below Knoxville (Lewis), down to Rathburn, Ham- 

 ilton Co. (Walker collection), and from the lower Clinch, up to 

 Agee, Campbell Co. (where it intergrades with conradi) ; and it is 

 in French Broad River, at Boyd Creek, Sevier Co. 



