UNITED STATES. 47 



large, without anv pai)illae on the edges. Super-anal 02)ening rather small and united 

 for some distance below. Anus somewhat corrugate. Color of the mass whitish. 



Einhnjonic shell is subtriangular and nearly allied to marginata. Journ. Acad. Nat. 

 Sci., New Ser., Vol. 4, pi. 5, fig. 28, Obs., Vol. G, pi. 5, fig. 28. 



Remarks. — I have received a number of specimens from different southern habitats 

 all bearing the same characters. The species is closely allied to M. undtikda 

 {Alasmodonta Say) so common to our eastern rivers. It diflfers from it in being more 

 triangular, loss oblique, l^ss ponderous, and in having the teeth single and not double 

 in the left valve as in undtdafa. The undulations of the beaks, although of the same 

 character, are smaller, and the posterior slope is flatter and wider. The angle on the 

 umbonial slope is also much more strongly marked. 



Margaritana Coxnasaugaensis. pi. 32, fig. 113. 



Testa Itevi, obovata, postic6 inflata, antic6 et po.stice rotundatS, valde inaequilaterali ; valvulis pertenuibus ; 

 natibus prominulis, ad apices run;oso-undulatis; epidermide viridi-lutea, postice obsolete radiata; 

 dentibus cardinalibus parvis, couiprcsso-tubereulatis, in utnxiue vulvulo unicis ; margarita ca?ruleo- 

 alba et iridescente. 



Shell smooth, obovate, inflated behind, rounded before and behind, very inequilateral ; 

 valves very thin ; beaks a little prominent and rugosely undulate at the tips ; epidermis 

 greenish yellow, obsoletely radiate behind ; cardinal teeth small, compressed, tuber- 

 culate and single in both valves ; nacre bluish white and iridescent. 

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



Ilab. — Connasauga River, one of the head waters of the Alabama Eiver, in Gilmer 

 County, Georgia, Bishop Elliott. Tennessee, J. G. Anthony. 



My cabinet and cabinets of Bi.shop Elliott and Mr. Anthony. 

 Diam. 1, Length 1-4, Breadth 2-4 inches. 



Shell smooth, obovate, inflated behind, rounded before and behind, suberaarginate 

 at base, very inequilateral ; substance of the shell very thin ; beaks a little prominent' 

 with three or four large, transverse undulations on each of the tips ; ligament rather 

 long and moderately thick ; epidermis greenish yellow, obscurely radiate behind, 

 striate before and with very distant, well defined marks of growth ; umbonial slope 

 mucii inflated and rounded ; posterior slope raised into a carina and furnished with 

 two obscure impressed lines in each valve, from the beaks to the posterior margin ; 

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

 cicatrices large, confluent and very slightly impressed ; posterior cicatrices confluent, 

 large and scarcely discernible ; dorsal cicatrices placed under the plate, above the 

 cavity of the beaks; cavity of the shell deep and rounded ; cavity of the beaks shallow 

 and subangular ; nacre bluish white and very iridescent. 



liemarlis. — There is only a single specimen of this species before me, and, unfortu- 

 nately, I have not had the opportunity of examining the soft parts. It is not closely 



