FRESH W \ TE8 AND LAND SHELLS. 81 



I'mh C0MPRESSIS3IMTJS. PI. VIII. Fig. 23. 



7'i v/ tewt, mbtriangvdari, valde compressa; valvulis crassia; natibua compresaia; dentibus cardinalibus 

 p arv latis; lateralibtts magnis, crassis curviaque ; margarita alba. 



Shell smooth, subtriangular, very much compressed; valves thick; beaks compressed ; cardinal teeth very- 

 small, crenalate; lateral teeth large, thick, and curved: nacre white. 



Hab. Holston River, Tennessee. President Estabrook. 



My cabinet and cabinets of Mr. Estabrook and Dr. Griffith. 

 Diam. .8, Length 1.6, Breadth 2.6 inches. 



Shell smooth, subtriangular, very much compressed, sub-arcuate at base, and angular 

 behind; substance of the shell very thick, very irregular on the interior surface, thick 

 before and thinner behind; beaks very much compressed and slightly prominent; ligament 

 and large; cardinal teeth very remarkably small, crenulate, single in the right and 

 double in the left valve; lateral teeth very large, thick, and curved; anterior cicatrices 

 distinct; posterior cicatrices distinct; dorsal cicatrices placed along the edge of the plain 

 over the cavity of the beaks; cavity of the shell exceedingly shallow; cavity of the beaks 

 very shallow and subangular; nacre white. 



Remarks. — This is a very remarkable species, being more compressed than any Unio 

 which has come under my notice. Both the specimens before mc arc unfortunately without 

 any epidermis, except along the basal margin, and there too much injured to display any 

 character. Although so completely eroded over the whole exterior surface, they were 

 taken alive, and the interior is fresh. The cavity of the shell being very small, the 

 included soft parts must have been unusually small. The interior aspect of the shell 

 is peculiar, the surface of the nacre being very irregular, almost varicose. In each of 

 the four valves before me there is an impressed line running from the inner side of the 

 great posterior cicatrix up to the cavity of the beak. The form, in younger and more 

 perfect specimens, will, I presume, be found to be more elliptical. It is likely that this 

 species prefer-- a gravelly bottom and rapid current. It is most nearly allied to U.pha- 

 '.8, I lild. 



I'vm pulvinulus. PI. VIII. Fig. 24. 



'/'. i,i I . i .'. elliplii 1, in/laid; valvulis crassis; nalibus prominentibus ; epidermidt tenebroaO'fuacA ; dentibus 

 cardinalibut mimUissimis ; laleralibus brevis rectisque; m < albd <i iridescente, 



Shell smooth, elliptical, inflated ; valves thick; beaks prominent; epidermis dark-brown; cardinal teeth very 

 small; lateral teeth short and straight; nacre white and iridescent. 



Hab. Tuscaloosa and Coosawattee River, Murray County. Alab. B. W. Budd, M. D. 



My cabinet and cabinets of Dr. Budd and Dr. Griffith. 

 Diam. .6, Length .9, Breadth 1.2 inches. 



Shell smooth, elliptical, inflated, obtusi l\ angular on the umbonial slope and slightly 



flattened on the sides, inequilateral; substance of the shell thick before and thin behind; 



beak rather prominent and full; ligament very short and thin; epidermis dark-brown, 



ining and without rays; cardinal teeth very small, erect and pointed, single in 



the right and double in the left valve; lateral teeth Bhort and straight; anterior cicatrices 



VOL. X. 21 



