NEW UNIONIDyE OF THE UNITED STATES. 99 



the same form. It is, however, a larger species and the males are more angular pos- 

 teriorly. The female shell is smaller than the male, and is enlarged on the umbonial 

 slope, and dilated at the posterior basal margin. None of the specimens were perfect 

 enough to observe undulations at the beaks. In outline it is very closely allied to 

 cariosus, Say, but differs entirely in the color of the epidermis, in the greater thick- 

 ness of the substance of the shell and in the rays, as well as having a much more de- 

 pressed posterior slope. Some of the old specimens of Spillmanii are so dark a brown 

 as to be almost black, and these are entirely without rays. Perfect and younger 

 specimens have all more or less nearly equidistant, well defined rays over the whole 

 disk. Among thirteen specimens three only have white nacre, the remainder bein°- 

 of a fine salmon color. The cardinal tooth in the right valve is disposed to duplica- 

 tion. That of the left is perfectly duplicate. I have great pleasure in naming this 

 species after Wm. Spillman, M. D., to whom I am under many obligations for several 

 envois of the fresh water mollusca of his part of the State of Mississippi. 



Unio paupercdlus. PI. 15, fig. 247. 



Testa laevi, subrotunda, subcompressa, subequilaterali, postice subrotunda, antice rotunda; valvulis sub- 

 crassis, antice crassioribus ; natibus proniinulis ; epidermide luteo-cornea, eradiata; dentibus eardinali- 

 bus magnis, elevatis, decussatis ; lateralibus brevissimis, obliquis reetisque ; margarita alba et iri- 

 descente. 



Shell smooth, subrotund, somewhat compressed, nearly equilateral, nearly round 

 behind, round before ; valves somewhat thick, thicker before ; bea'ks slightly promi- 

 nent ; epidermis yellowish horn color, without rays ; cardinal teeth large, raised, de- 

 cussate ; lateral teeth very short, oblique and straight; nacre white and iridescent. 

 Proc. Acad. Nat. Sci. 18(31, p. 39. 



Hob. — Stream near Columbus, Mississippi. Wm. Spillman, M. D. 



My cabinet and cabinet of Dr. Spillman. 

 Diam. -6, Length "9, Breadth M inch. 



Shell smooth, subrotund, somewhat compressed, nearly equilateral, nearly round 

 behind, round before; substance of the shell somewhat thick, thicker before • beaks 

 slightly raised ; ligament very short, thick and dark brown ; epidermis yellowish horn 

 color, without rays, with close, equidistant lines of growth; umbonial slope somewhat 

 raised and very obtusely angular; posterior slope carinate, subcordate ; cardinal teeth 

 large, raised and much divided; lateral teeth very short, oblique, straight, and leaving 

 a wide plate between them and the cardinal teeth ; anterior cicatrices distinct small 

 and deeply impressed; posterior cicatrices confluent, small and well impressed • dorsal 

 cicatrices placed under the plate at the base of the cardinal tooth ; cavity of the shell 

 rather shallow and rounded ; cavity of the beaks rather deep and acutely angular ■ 

 nacre white and iridescent. 



