536 ORTMANN—NAYADES OF 
10. FUSCONAIA BARNESIANA BIGBYENSIS (Lea), 1841. 
Unio bigbyensis Lea, ’41.—Unio estabrookianus Lea, ’45.—Unio fas- 
sinans Lea, ’68.—Unio fascinans Pilsbry & Rhoads, ’96.—Pleuro- 
bema fassmans rhomboidea Simpson, ’00.—Fusconaia estabrook- 
1ana Goodrich, ’13, p. 93.—Pleurobema bigbyense, P. fassinans 
and var. rhomboideum, P. estabrookianum Simpson, ’14, pp. 756, 
797, 798, 803.—Fusconaia barnesiana bigbyensis Ortmann, ’17, 
Pp. 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 rhomboideum 
represent normal specimens, the former with distinct, the latter with 
indistinct or missing rays. U. estabrookianus 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 Pleurobema oviforme 
argenteum. 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 drainege: 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 
