756 PLEUROBEMA 
The type of Unio pudicus is a young shell and is brighter 
and more compressed than that of Unio lyonit, which is an 
adult shell. Since writing the Synopsis I have had an oppor- 
tunity of examining a number of shells of the U. pudicus and 
it seems to me to he identical with lyonii. The form is less 
triangular than bigbyense and a little more inflated. 
PLEUROBEMA BIGBYENSE (Lea). 
Shell subcompressed, subtriangular or subrhomboid, inequi- 
lateral, subsolid; beaks high and moderately full, their sculp- 
ture a few strong, uneven, subnodulous ridges that curve up 
behind; anterior end rounded ; base line lightly curved; outline 
of the dorsal slope curved, raised to an angle behind the liga- 
ment; posterior ridge rounded or imperfectly double, ending 
in a blunt point near the base of the shell; surface nearly 
smooth ; epidermis greenish-yellow with numerous green, en- 
tire or broken rays, sometimes with broken bands of green; 
the whole bright and glossy; pseudocardinals radial, two in 
the left valve and three in the right; laterals two in the left 
valve and a somewhat double one in the right; muscle scars 
rather small, impressed: beak cavities shallow; nacre white. 
Length 52, height 39, diam. 18 mm. 
Tennessee River drainage; Indian Territory? Texas? The 
two last localities very doubtful. 
Type locality, Big Bigby Creek, Maury Co., Tenn. 
Umolbigbyensis Lea,-Pr Am. Phil, Soe, Hy as4i.ep. 305ehi 
Am, Phil.-Soc., VILL 1843, p; 237,.pl: sox, hie BOs 
ITT, 1842, p. 75, pl. xxu, fig. 51.—CuHeENu, Ill. Conch., 1858, 
pl. xxu, figs. 5, 5a, 5b.—Kuster, Conch. Cab. Unio, 1862, p. 
270, pl. xciv, fig. 3—Sowersy, Conch. Icon., XVI, 1866, pl. 
ST Aey 2277. 
Margaron (Unio) bigbyensis Lea, Syn., 1852, p. 24; 1870, p. 
38. 
Pleurobema bigbyensis Simpson, Syn., 1900, p. 75T. 
This species seems allied by its form to the argenteum 
group, but the coler pattern is that of the clava group. Its 
form is much like that of P. argenteum, but that species 1s 
dull and rarely exhibits even traces of rays. 
