742 PLEUROBEMA 
narrow broken rays, and shining, often dull and feebly raye., 
in old shells; pseudocardinals irregular, rough, two in the left 
valve and three in the right, the anterior and posterior teeth 
in the right feeble; two laterals in the left valve and a some- 
what double one in the right; beak cavities compressed, deep 
for a Pleurobema; nacre white; muscle scars deep, small. 
Length 45, height 45, diam. 35 mm. 
Length 53, height 48, diam. 31 mm. 
length 45, height 40, diam. 3: mm. 
‘ennessee River system. 
Type locality, Holston River, Tenn., and Tennessee River, 
Florence, Ala. 
Unio edgarianus Lea, Pr. Am. Phil. Soc., I, 1840, p. 288; Tr. 
Am. Phil: Soc, Vil 1842" p. 214. pl axe noe 0 -e@)ns. mien 
1842, p. 52, pl. xv, fig. 30.—CueENu, Ill. Conch., 1858, pl. 
XXIX, figs. 5, 5¢, 5b>—Kustrr, Conch. Cab., 1861, p. 213, 
pl. Lxx, fig. 5——Muscrave, Phot. Conch., 1863, pl. 11, fig. 6. 
—Rerve, Conch. Icon., XVI, 1864, pl. xv, fig. 65. 
Margaron (Unio) edgarianus Lea, Svn., 1852, p. 25; 1870, p. 
39. 
Pleurobema edgarianus SIMPSON, Syn., 1900, p. 747. 
Unio obuncus Lea, Pr. Ac..N: Se, Phila., 1, 1871, ‘p. 1925 Ji: 
Ac: Nw Ser Phila: Vill, 1874p. 9;.pl ais fears Oss axe 
1874, Pe 13s split, fies <5. 
Unio andersonensis Lea, Pr. Ac. N. Sci. Phila., II, 1872, p. 
rs; jl Ac. N. Sew Phila., VIL 1874, p..30,.ple in ie 3 4, 
Obs:, <I, 18745 p. 40; plo; fe. 32. 
The specimens placed by Dr. Lea under Unio edgarianus 
show a wide degree of variation in form and color. I have 
placed in the synonymy his Unio obuncus and andersonensis, 
which differ less from edgarianus than specimens of that spe- 
cies do among themselves. The young shells are mostly bright 
and rayed, they usually become dull and feebly rayed when 
old and at this stage they may be brown or tawny colored. 
The beaks are fuller and less sharply elevated than in bourni- 
anum, the beak cavities are deeper, in fact they are unusually 
deep for a Pleuwrobema; the posterior ridge is not so low nor 
is it placed so near the posterior line as it is in bournianum. 
