NEW UNIONIDJE OF THE UNITED STATES. L05 



most nearly allied to M. Spillmanii, herein described, but it cannot be confounded with 

 that species. The color of the epidermis is totally different. It is rather more oblique, 

 and not so much inflated. The undulations at the tips of the beaks differ from those 

 of Spillmanii, being more concentric. Those of Alabamemis being few, coarse and 

 nearly parallel with the plane of the dorsal line. The epidermis is bright and looks 

 almost as if varnished. Young and perfect specimens may be found to be rayed, but 

 the specimen before me has none on the sides; there are a few indistinct capillary 

 ones on the posterior slope. The tooth of the left valve has not a natural appearance, 

 being irregularly tuberculate and slightly duplicate, while that in the right valve is 

 lamellar and obtusely pointed. The figure will be observed to be arcuate at the base, 

 but this arises evidently from an injury. It will be observed that the lines of growth 

 above are regular and have no emargination at the sides. 



Margaritana Spillmanii. PI. 17, fig. 252. 



Testa Isevi, obovata, superne valde inflata, postice obtuse angulata, subfcquilaterali ; valvulis subcrassis, 

 antice crassioribus; natibus prominentibus, tumidis, ad apices rugoso-undulatis; epidermide vel rufn- 

 fusca vel tenebroso-fusea, obsolete radiatS, micante ; dentibus cardinalibus parvis, tuberculato-compn --i-, 

 in utroque valvulo singulis; margarita alba et iridescente. 



Shell smooth, obovate, very much inflated above, obtusely angular behind, subequi- 

 lateral; valves rather thick, thicker before; beaks somewhat prominent, swollen, 

 rugosely undulate at the tips; epidermis reddish or dark brown, obscurely radiate, 

 shining ; cardinal teeth small, compressed, tuberculate and single in both valves ; 

 nacre white and iridescent. 



Proc. Acad. Nat. Sci. 1858, p. 138. 



Hah. — Tombigbee Eiver, near Columbus, Mississippi. Wm. Spillman, M. D. 



My cabinet and cabinet of Dr. Spillman. 

 Diam. T5, Length 2, Breadth 3'7 inches. 



Shell smooth, obovate, very much inflated above, obtusely angular behind, sub- 

 equilateral ; substance of the shell rather thick, thicker before ; beaks somewhat 

 prominent, swollen rugosely undulate at the tips ; ligament rather short and dark 

 brown ; epidermis reddish or dark brown, obscurely rayed, shining, with very distant 

 marks of growth ; umbonial slope very much inflated and rounded ; posterior slope 

 wide, elliptical, flatfish, with two raised lines from the tips to the posterior margin ; 

 cardinal teeth small, compressed-tuberculate and single in both valves ; anterior 

 cicatrices distinct, large and moderately impressed ; posterior cicatrices continent, 

 very large and slightly impressed; dorsal cicatrices placed above the centre of the 

 cavity of the beaks; cavity of the shell very deep and wide; cavity of the beaks 

 rather deep and subangular; nacre white and iridescent. 



Soft 'parts. — Branchial uterus occupied the whole length of the outer branchiae, 



