534 ORTMANN—NAYADES OF 
drainage of North Alabama, and, also here, cor is in the Tennessee 
proper and the lower parts of the larger tributaries (Elk, both Flint, 
and Paint Rock Rivers), while in the upper parts, at least of Paint 
Rock River, it passes into the analoga-form. 
GROUP OF FUSCONAIA BARNESIANA (Lea). 
Forms: of this group have been listed by Lewis (’71) as U. bar- 
nesianus, pudicus, and tumescens. In Simpson’s papers (’oo and 
14), they stand under Pleurobema, and their proper position and 
mutual relation have not at all been understood. 
All these shells belong to Fusconaia, but form a separate group 
within this genus, distinguished from the other species by very shal- 
low beak cavities, and the peculiar color of the eggs and placente, 
which is darker or lighter purplish-black, or some similar shade (see 
Ortmann, ’17). 
Also here we have the phenomenon that flat and compressed 
forms are found in the headwaters, swollen forms in the larger 
rivers, with the intergrades between them in the rivers of medium 
size. The transition is complete and very gradual, so that it is ex- 
tremely difficult to draw separating lines. The division into three 
local (or rather ecological) races, introduced here, is entirely arbi- 
trary, but justified to a degree by the old division into “ species,’ and 
the fact that it is just such an intergrade which has first received a 
name (barnesianus). The difficulty of classifying these forms be- 
comes greater yet, because these shells vary not only in obesity, but 
also in general outline, development of beaks, and color markings. 
I shall distinguish three forms: barnesiana bigbyensis, with the 
diameter less than 40 per cent. of the length; barnesiana, with the 
diameter from 40 to 49 per cent.; and barnesiana tumescens, with 
the diameter of 50 per cent. and over. 
g. FUSCONAIA BARNESIANA (Lea), 1838. 
Unio barnesianus Lea,’38.—Unio meredithi Lea, ’58.—Unio pudicus 
Lea, *60.—Unio lyomi Lea, ’65.—Unio barnesianus and pudicus 
Lewis, *71.—Unio tellicoensis Lea, ’72—Unio lenticularis Lea, 
’72,—Pleurobema barnesianum, pudicum, lenticulare, meredithi 
