NEW UNIONIDiE OF THE UNITED STATES. 103 



much smaller and the teeth are delicate, very small, and not crenulate ; nor is it so 

 much inflated. In the soft parts it differs much, particularly in the anal opening- 

 being furnished with well defined papillae. 



Unio curttjs. PI. 17, fig. 253. 



Testa lasvi, obliqua, ad umbones valde tumida, antice truncata, postice obtuse angulata, valde intequilaterali : 

 valvulis percrassis, antice crassioribus; natibus elevatis, crassis, fere tcrminalibus ; epiderinide vel 

 tenebroso-castanea vel tenebroso viridi, ad apices virescens, obsolete radiata ; dentibus cardinalibus 

 subgrandibus, compressis, acuminatis, obliquis ; lateralibus crassis subcurvisque; niargarita argentea. et 

 iridescente. 



Shell smooth, oblique, much swollen at the beaks, truncate before, obtusely angular 

 behind, very inequilateral ; valves very thick, thicker before ; beaks elevated, thick, 

 nearly terminal ; epidermis dark chestnut or dark green, greenish towards the beaks, 

 obscurely radiate ; cardinal teeth rather large, compressed, pointed and oblique ; lateral 

 teeth thick and somewhat curved ; nacre silver white and iridescent. 

 Proc. Acad. Nat. Sci. 1859, p. 112. 



Hob. — Tombigbee River, Columbus. Mississippi. Win. Spillman, M. D. 



My cabinet and cabinet of Dr. Spillman. 

 Diam. 1, Length 1-2, Breadth 1-G inch. 



Shell smooth, oblique, very much swollen at the beaks, truncate before, obtusely 

 angular behind, very inequilateral, depressed before the umbonial slope ; substance 

 of the shell very thick, thicker before; beaks elevated, thick, nearly terminal ; liga- 

 ment short, thick and light brown ; epidermis dark chestnut color or dark green, green- 

 ish towards the beaks, obscurely rayed, with rather distant marks of growth ; umbonial 

 slope slightly raised and subangular ; posterior slope very narrow, with two obscure 

 lines leading from the tips to the posterior margin ; cardinal teeth rather large, com- 

 pressed, pointed, crenulate and oblique ; lateral teeth thick and somewhat curved ; 

 anterior cicatrices distinct; posterior cicatrices distinct; dorsal cicatrices placed on the 

 under side of the plate and posterior to the cardinal tooth; cavity of the shell rather 

 deep and rounded ; cavity of the beaks shallow and obtusely angular ; nacre silver 

 white and very iridescent behind. 



Soft parts. — There were ova in the branchial uterus, and the ovarium of one, but 

 only in the ovarium of the other female. The uterus occupied the whole length of the 

 outer branchiae. BrancMce large, semi-circular, outer ones rather the larger, free nearly 

 the whole length of the abdominal sack. Palpi small, thin, subtriangular, pointed at 

 the end, united on the posterior edges only at the upper part. MantU very thin, 

 slightly thickened at the margin. Branchial opening rather small, with small brown- 

 ish papillae. Anal opening rather large, with very small papillae. Super-anal open- 

 ing small, colored on the inner margin and united below. Color of the mass whitish. 



