FRESH WATER AND LAND SHELLS. 20 
Hab. Alexandria, Louisiana, J. Hale, M.D. 
My cabinet and cabinets of Dr. Hale, and Acad. of Nat. Science. 
Diam. .7, Length 1.38, Breadth 2.2 inches. 
Shell smooth, elliptical, rather convex, inequilateral, rounded behind; substance of the 
shell rather thin; beaks small, slightly prominent, undulated at the tip; hgament rather 
long and thin; epidermis shining, black, striate, in the young radiate all over the disk; 
marks of growth rather distant; posterior slope compressed into a small carina; umbonial 
slope slightly raised and rounded; cardinal teeth rather large, somewhat compressed, 
oblique, acuminate, crenulate and double in both valves; lateral teeth long, lamellar, some- 
what curved and separated from the cardinal tooth; anterior cicatrices distinct; posterior 
cicatrices confluent; dorsal cicatrices placed near the edge of the plate and on the car- 
dinal tooth; cavity of the shell rather shallow; cavity of the beaks shallow and subrotund; 
nacre white and very iridescent. 
Remarks—This species is nearly allied to U. Haleianus, (Nobis,) but differs in the 
outline, and is not so wide; in the epidermis, which is blacker and more shining, and in 
the beaks, the undulations of which are more numerous and less regular. It belongs to 
that group of which U. Nashvillianus, (Nobis,) may be considered the type, the beaks being 
very much, in their undulations, of the character of that species. All the adults, male 
and female, of which I have many specimens, are very black and apparently without rays, 
but when held up to a strong light, delicate obscure rays may be observed, particularly 
about the umbonial slope. In the individuals of one-third growth and less, the epidermis 
is dark-green and covered with rays. The female differs very much in outline from the 
male, and is much inflated on that portion of the disk which tends to the posterior basa] 
margin. In this very much enlarged female characteristic, this species resembles Nash- 
villianus, Haleianus and parvus. This enlargement makes that margin obliquely truncate. 
Unio Prevostianus. Pl. XIX. Fig. 24. 
Test levi, ellipticd, subcompressd, valde inequilaterali, posticé rotundata; valvulis pertenuibus; natibus 
parvis, prominulis, ad apices undulatis ; epidermide luted, tenebroso-radiata, polita; dentibus cardinalibus 
parvissimus, compressis, perobliquis; lateralibus longis, lamellatis subcurvisque; margarita ceruled et 
tridescente. 
Shell smooth, elliptical, rather compressed, very inequilateral, rounded behind; valves very thin; beaks small, 
slightly prominent, undulated at the tip; epidermis yellow, very much and darkly radiated, polished; cardinal 
teeth very small, compressed, very oblique; lateral teeth long, lamellar and somewhat curved; nacre bluish and 
iridescent. 
Hab. Eutowah River, Georgia, Mr. C. M. Wheatley. 
Cabinet of Mr. Wheatley. 
Diam. .7, Length 1.2, Breadth 2.3 inches. 
Shell smooth, elliptical, rather compressed, very inequilateral, rounded behind; substance 
of the shell very thin; beaks small, slightly prominent, undulated at the tip; ligament long 
and thin; epidermis polished, yellow, with numerous broad dark-green rays covering 
nearly the whole disk, lighter before and very dark behind, with very distant marks of 
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