536 ORTMANN— NAYADES OF 



lO. FUSCONAIA BARNESIANA BIGBYENSIS (Lea), 184I. 



Unio bigbyensis Lea, '41. — Unio estabrookiamis Lea, '45. — Unio fas- 

 siiians Lea, '68. — Unio fascinans Pilsbry & Rhoads, '96. — Plciiro- 

 bema fassinans rhomboidea Simpson, '00. — Fusconaia estabrook- 

 iana Goodrich, '13, p. 93. — Pleurobcma bigbyense, P. fassinans 

 and var. rhomboideum, P. estabrookianum Simpson, '14, pp. 756, 

 797, 798, 803. — Fusconaia barnesiana bigbyensis Ortmann, '17, 

 P-59- 



This is the form of the headwaters and small tributaries of the 

 Tennessee system, with a diameter of less than 40 per cent, of the 

 length of the shell. U. bigbyensis and P. fassinans rhoniboideum 

 represent normal specimens, the former with distinct, the latter with 

 indistinct or missing rays. U. estabrookiamis is founded upon very 

 large, somewhat distorted specimens; and the only type (examined 

 in Washington) of U . fassinans is an exceptionally elongated, rather 

 large specimen without rays. 



Also in this form we have the phenomenon that the compressed 

 headwaters shell, so to speak, gains in circumference what it has 

 lost in diameter. The var. bigbyensis grows much larger than the 

 forms farther downstream. It is very variable in size, shape, color, 

 and sometimes it is hard to distinguish it from Pleiirobema oviforme 

 argenteuni. Generally, darker (brownish) color of epidermis, with 

 fine rays (when present), forming no blotches, and a more central 

 position of the beaks distinguish F. barnesiana bigbyensis. Of 

 course, the anatomy is entirely different. 



This race is very generally distributed over the whole upper 

 Tennessee drainage, but disappears in the larger rivers. It often is 

 in very small streams of the headwaters (North Fork Powell, and 

 other small streams in the Powell drainage ; in the Clinch at Taze- 

 well, Va. ; Big Moccasin Creek, all three forks of the Holston, and 

 also Laurel Creek, Watauga River, and Little Pigeon River ; Second 

 Creek at Knoxville ; Sale Creek in Rhea Co. ; Little River ; Abram 

 Creek in Blount Co. ; Tellico River ; Spring Creek, Polk Co., and 

 Cane Creek, McMinn Co.). 



As has been stated, even at the uppermost localities, in very small 

 creeks, F. barnesiana in its typical form may be present, and may be 



