100 NEW UN1UNU>/K OF THE UNITED STATES. 



Remarks. — This small species looks like some of the small depauperated specimens 

 of rubiginosus (nobis) ; but while its angular umbonial slope gives it a triangular ap- 

 pearance in outline, it is really subrotund. In outline, it is nearest to petrinus, Gould, 

 but cannot be confounded with that species, being much smaller and thinner, and not 

 so regularly round. The cardinal teeth are remarkably large for so small a species, 

 and the- lateral teeth remarkably small. The nacre is unusually thin in the middle 

 towards the base, being very iridescent there. None of the beaks were nearly per- 

 fect, and therefore the character of the undulations of the tips could not be observed. 

 The largest of five specimens was only an inch long and an inch and three-tenths 

 wide. The plate between the cardinal and lateral teeth is remarkably large. 



Unio cinnamomicus. PL 16, fig. 248. 



Testa leevi, elliptica, inflata, ad umbones tumida, inasquilaterali, postice" angulata, antice rotunda; valvulis 

 subcrassis, antice crassioribus ; natibus subprominentibus ; epidermide cinnamomiea, interne" striata, 

 eradiat&; dentibus cardinalibus parviuseulis, erectis, subcompressis crenulatisque ; lateralibus curtis 

 subrectisque ; margarita albida et valde iridescente. 



Shell smooth, elliptical, inflated, swollen towards the beaks, inequilateral, angular 

 behind, round before; valves somewhat thick, thicker before ; beaks somewhat promi- 

 nent; epidermis cinnamon brown, striate below, without rays; cardinal teeth rather 

 small, erect, somewhat compressed and crenulate; lateral teeth short and nearly 

 straight ; nacre whitish and very iridescent. 

 Proc. Acad. Nat. Sci. 1861, p. 39. 



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



My cabinet and cabinet of Dr. Spillman. 

 Diam. -7, Length 1, Breadth 1-4 inch. 



Shell smooth, elliptical, inflated, swollen on the umbones, inequilateral, angular 

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

 beaks somewhat prominent ; ligament short, rather thin and dark brown ; epidermis 

 cinnamon brown, darker and striate below, above brighter and smooth, without rays, 

 and with very distant marks of growth ; umbonial slope slightly raised and very ob- 

 tusely angular; posterior slope cordate, slightly paler in color, very , slightly raised, 

 with two capillary lines from beak to margin on each valve ; cardinal teeth rather 

 small, erect, somewhat compressed, corrugate and crenulate ; lateral teeth short and 

 nearly straight ; anterior cicatrices distinct, rather small and well impressed ; poste- 

 rior cicatrices distinct, rather small and slightly impressed ; dorsal cicatrices placed 

 above the centre of the cavity of the beaks ; cavity of the shell rather shallow and 

 rounded ; cavity of the beaks rather shallow and obtusely angular ; nacre whitish 

 and very iridescent. 



Bemarfcs. — This is a very distinct little species, which is not likely to be confounded 

 with any other I am acquainted with. I have two specimens before me. None were 



