28 DESCRIPTION OF NEW 
Shell smooth, elliptical, somewhat inflated, rather inequilateral, rounded behind; sub- 
stance of the shell thin; beaks small, slightly prominent; ligament rather short and thin; 
epidermis yellowish, with rather small, somewhat distant rays on the posterior portion of 
the disk, and with strong distant marks of growth; posterior slope rather depressed; 
umbonial slope gradually rounded; cardinal teeth much compressed, oblique, acuminate, 
double in both valves; lateral teeth thin, rather long, lamellar, nearly straight and sepa- 
rated from the cardinal teeth; anterior cicatrices distinct; posterior cicatrices confluent ; 
dorsal cicatrices placed rather below the centre of the cavity of the beaks; palleal cica- 
trix impressed anteriorly; cavity of the shell rather deep; cavity of the beaks rounded; 
nacre white and iridescent. 
Remarks.—I have before me but a single specimen of this shell, and with older, younger 
or more perfect specimens, the characters are very likely to vary. In nearly all its cha- 
racters it is most nearly allied to & obscurus, (Nobis.) It differs in being less angular at 
the posterior margin, in being a thinner shell, and in having the teeth lamellar and thin. 
The colour of this specimen is white, while the odscurus is usually partly purplish. 
Unio Reeveranus, Pl. XX. Fig. 28. 
Testa levi, elliptica, inflata, valdé incquilaterali, postice obtuso-angulata ; valvulis tenuibus 3 natibus parvis, 
prominulis; epidermide luted, radiata; dentibus cardinalibus parvis, subobliquis; lateralibus longis, tenui- 
bus subcurvisque; margarita alba et iridescente. 
Shell smooth, elliptical, inflated, very inequilateral, obtusely angular behind; valves thin; beaks small, a little 
prominent; epidermis yellowish, radiated; cardinal teeth small, rather oblique; lateral teeth long, thin and curved; 
nacre white and iridescent. 
Hab. Alexandria, Louisiana, J. Hale, M. D., and Prof, Powell. 
My cabinet and cabinets of Dr. Hale and Prof. Powell. 
Diam. 1.1, Length 1.6, Breadth 2.9 inches. 
Shell smooth, elliptical, inflated, very equilateral, obtusely angular behind; substance 
of the shell thin, thicker before; beaks small and a little prominent; ligament rather long 
and somewhat thick; epidermis yellowish, shining, with numerous green rays over the 
posterior portion of the shell and distant lines of growth; posterior slope rather com- 
pressed into a carina; umbonial slope but slightly raised and rounded; cardinal teeth small, 
rather oblique, double in the right and slightly double in the left valve; lateral teeth long, 
thin, somewhat curved, widely separated from the cardinal teeth; anterior cicatrices dis- 
tinct; posterior cicatrices confluent; dorsal cicatrices placed on the under side of the 
plate; palleal cicatrix impressed; cavity of the shell deep; cavity of the beaks rather shal- 
low and subangular; nacre white and iridescent. 
Remarks.—Among the many interesting shells sent to me by Dr. Hale and Prof. Powell, 
were two specimens which are now before me. ‘The larger one, which is here figured, is 
apparently a male, the other a female. They differ much, the latter being much smaller, 
but apparently grown. It is very much broader on the posterior portion, and somewhat 
truncate. In colour and form of rays the two specimens are the same. Neither of them 
are by any means perfect, being much eroded towards the beaks, the character of which, 
