UPPER TENNESSEE DRAINAGE. 589 



Thus this is undoubtedly one of the rarest species of Truncilla, 

 and its distribution should be studied more closely. 



Type locality: Holston River, Tenn. (topotype examined). 



82. Truncilla propinoua (Lea), 1857. 



Unio propinqiiiis Lea, '57. — Unio propinqims Lewis, '71. — Unio 

 propinquus Pilsbry & Rhoads, '96. — Truncilla propinqua Simp- 

 son, '14, p. 27. 



Reported, ^by Lewis, from Tennessee River, Knox Co., and from 

 the Clinch by Call. Pilsbry & Rhoads give it from the Tennessee at 

 Knoxville, the Holston at Boyd Island, near Knoxville, and from the 

 Clinch at Patton's Ferry, Roane Co. The Carnegie Museum pos- 

 sesses it from the Tennessee, Knox Co. (Smith coll.), and I found it 

 myself in the Clinch at Edgemoor and Clinton, Anderson Co., Tenn. 

 Type locality: Florence and Tuscumbia, Ala. (topotypes ex- 

 amined). 



83. Truncilla torulosa (Rafinesque), 1820. 



Amblema torulosa and gibbosa Rafinesque, '20. — Unio perplexus 



Lewis, '71. — Truncilla perplexa Simpson, '14, p. 24. — ■Truncilla 



torulosa Vanatta, '15, p. 550. 



The identity of torulosa and gibbosa with perplexus has been in- 

 dicated by Conrad ('34), and he selected the name of torulosa. Al- 

 though he later ('36) uses gibbosus (and so do Agassiz and Reeve), 

 the first selection has to stand. 



The typical T. torulosa has a radial row of prominent knobs 

 across the middle of the shell. But these knobs vary greatly, and in 

 the upstream direction, they have the tendency to become reduced, 

 finally disappearing, thus passing into the condition seen in the next 

 form. 



Restricted to the larger rivers. It turns up in the Tennessee at 

 and below Knoxville (Lewis), and continues down the river, but is 

 hardly found above Knoxville. The Carnegie Museum has three 

 young specimens from near Knoxville (Hartman coll.), which have 

 distinct knobs. In addition, there is a specimen from Chattanooga, 

 Hamilton Co., Tenn. (Juny coll.), which is typical in all respects, 



