N'KW unionid/t; of the united states. io7 



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

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

 being furnished with well defined papilte. 



Unio curtus. pi. 17, fig. 2-33. 



Tcstri lajvi, obliijua, aJ umbones valdu tumida, antici; truncatri, postiee obtuse aD<;ulata, valdt- in.xriuilaterali ; 

 valvulis percr.issis, anticc crassioribus; natibus clevatis, crassis, fere terminalibus ; epidermide vel 

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

 subgraudibus, compressis, acuminatis, obliquis ; lateralibus crassis subcurvisfjue ; margarita argentea ct 

 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. 

 Hah. — Tombigbee River, Columbus. Mississippi. Wni. Spillman, M. D. 

 My cabinet and cabinet of Dr. Spillman. 

 Diam. 1, Length 12, Breadth IG 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 raj^ed, 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. Branchicc large, semi-circular, outer ones rather the larger, free nearly 

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

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

 slightly tliiokened at the margin. Bran fhial open in (j rather small, with small brown- 

 ish papilloj. AnaJ opening rather large, with very small papilla;. Super-anal open- 

 infj small, colored on the inner margin and united below. Color of the mjiss whitish. 



