UNITED STATES AND NORTHERN MEXICO. 31 



The second cartlinal tooth in the right valve is very small. In two of the specimens 

 very indistinct rays may be observed ; the other six have no trace of them. 



Unio castus. pi. 57, fig. 17 i. 



Testa laevi, obliqua, influU, inaefiuilaterali, postict* angulata, antice rotunda; valvulis crassiusculis, antic« 

 • crassioribus ; natibussubprominentibus; epidermiJe micante, luteo-viridi, radiata; dentibua cardinali- 

 bus subgrandibus, coiiipressoconicis, striatis creiiulatisqua ; lateralibu-i subbrevibus, rcctis, laraellatis 

 striatisque ; margarita alba et iridescente. 



Shell smooth, oblique, inflated, inequilateral, angular behind and round before ; 

 valves rather thick, thicker before; beaks rather prominent; epidermis shining, yel- 

 owish green and radiated;- cardinal teeth rather large, compressed-conical, striate and 

 crenulate ; lateral teeth rather short, straight, lamellar and striate; nacre white and- 

 iridescent. 



Pro. Acad. Nat. Sci. 1860, p. 306. 



Hab. — South Carolina. Prof. Tuomey. 



My cabinet and cabinet of Dr. Ilartman. 

 Diani. -7, Length 1-1, Breadth 1-6 inch. 



Shell smooth, oblique, inflated, inequilateral, angular behind and round before; 

 substance of the shell rather tliick, thicker before; beaks somewhat prominent; 

 ligament short, thin and dark brown ; epidermis yellowish green, shining, radiated, 

 and with distant marks of growth ; umbonial slope raised, obtusely angular.; posterior 

 slope slightly raised, j-ellowish with two slightly impressed lines in each valve from 

 the beaks to the posterior margin ; cardinal teeth rather large, compressed-conical, 

 striate, crenulate and disposed to be double in both valves ; lateral teeth rather 

 short, straight, lamellar and striate ; anterior cicatrices distinct and well impressed ; 

 posterior cicatrices distinct and moderately well impressed ; dorsal cicatrices placed 

 under the plate anterior to the cardinal tooth ; cavity of the shell deep and rounded; 

 cavity of the beaks rather shallow and angular ; nacre white and iridescent. 



Remarlcs. — A single specimen oidy is before me. The beaks being eroded, the 

 character of the tips cannot be given. In outline it is nearest to argenteus (nobis), 

 and Ravemlianm (nobis), but it may at once be distinguished from the former by its 

 being smaller, more inflated, having more distant marks of growth, and in being radiated. 

 From the latter by being smooth in the epidermis, being more inflated and greener, and 

 in having fine green rays over nearly the whole disk. It has much the aspect of 

 »/jer?As (nobis), the epidermis being nearly the same color, and both having rays ; but 

 it diflers much in the outline, menis not being oblique, but oblong, and rather smaller. 

 I owe to the kindness of Dr. Ilartman, of AVest Chester, Pennsylvania, the possession 

 of the specimen described and figured. He received it from Prof Tuomey, with only 

 the habitat of South Carolina, so that we do not know in what district or stream 

 exactly it inhabits. 



