﻿UNITED STATES. 39 



Unio .equatus. PL 19, fig. G9. 



Testa lsevi, elliptica, conipressix, postice biangulata et planulata, valde ina3quilaterali ; valvulis subcrassis ; 

 natibus prominulis ; epidermide tenebroso-castanea, radiata, ad umbones polita ; dentibus cardinalibus 

 subgrandibus, paulisper elevatis crenulatisque ; lateralibus sublongis, lamellatis subrectisque ; margarita 

 vel alba vel purpurea vel salmonis colore tincta et iridescente. 



Shell smooth, elliptical, compressed, very inequilateral, triangular and flattened 

 behind ; valves slightly thickened ; beaks a little prominent ; epidermis dark chestnut 

 color, radiated, shining on the umbones ; cardinal teeth rather large, somewhat erect 

 and crenulate ; lateral teeth long, lamellar and nearly straight ; nacre white, purple 

 or salmon color and iridescent. 



Proc. Acad. Nat. Sci. 1857, p. 170. 



Bab. — Buckhead Creek, Burke County, Georgia. Bishop Elliott. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. *9, Length 1*5, Breadth 2'7 inches. 



Shell smooth, elliptical, compressed, very inequilateral, biangular and flattened 

 behind and regularly rounded before ; substance of the shell slightly thickened ; liga- 

 ment rather long and thin ; epidermis dark chestnut color inclining to green, obscurely 

 radiated, polished on the umbones, dull and striate towards the margin ; umbonial 

 slope flattish, with an obtuse angle ; cardinal teeth rather large, somewhat erect, 

 crenulate and disposed to be double in both valves ; lateral teeth long, lamellar and 

 nearly straight; anterior cicatrices distinct, rather large and well impressed ; posterior 

 cicatrices confluent, large and slightly impressed ; dorsal cicatrices small and placed 

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

 wide ; cavity of the beaks very shallow and rounded ; nacre white, purple or salmon 

 color and iridescent. 



Soft Parts. — Branchial uterus not charged, but ova were found in the ova- 

 rium. Branchiae thin, very large, nearly semicircular, inner ones very much the 

 larger anteriorly, free more than half the length of abdominal sack. Palpi remarkably 

 small, thin, triangular, united only at the upper part of the posterior edges. Mantle 

 very thin, slightly thickened on the broad margin and slightly colored at the edge. 

 Branchial opening very large, bordered with black, with numerous small papillae on 

 the inner edges. Anal opening large, bordered with black and having very minute 

 papillae on the edge. Super-anal opening rather small, blackish on the inner edges, 

 not united below, but free with the anal opening. Color of the mass whitish. 



Remarks. — This species is perhaps nearest to fumatus (nobis,) but it leans to For- 

 besianus, (nobis,) a much thicker species. It is more compressed and more oval. It is 

 dark on the posterior slope. The two angles on the posterior margin are more separate 

 than in fumatus, and better defined. 



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