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pressed behind, emarginate; valves thick, thicker before ; beaks a little prominent; 

 epidermis dark brown, obsoletely radiate behind ; cardinal teeth rather large, erect 

 and obtusely conical, double in both valves ; lateral teeth rather long, somewhat 

 straight and rather thick ; nacre dark purple and iridescent. 



Proc. Acad. Nat. Sci. 1857, p. 32, as umbrosus, which name was preoccupied. 

 Hob. — Othcalooga Creek, Gordon County, Georgia. Bishop Elliott. 

 My cabinet and cabinet of Bishop Elliott. 

 Diam. '7, Length 1, Breadth 1-4 inches. 



Shell smooth, elliptical, ventricose, nearly equilateral, obtusely angular, com- 

 pressed behind and regularly rounded before, emarginate at posterior basal margin ; 

 substance of the shell thick, much thicker before ; beaks a little prominent, submedial ; 

 ligament short and rather thin ; epidermis very dark brown, slightly polished, obso- 

 letely radiate on posterior half, and with not very distinct lines of growth ; umbonial 

 slope rounded; cardinal teeth rather large, erect, crenulate and double in both 

 valves ; lateral teeth rather long, nearly straight and somewhat thick ; anterior cica- 

 trices very distinct and very much impressed; posterior cicatrices confluent and 

 deeply impressed ; dorsal cicatrices rather large, deeply impressed and placed in the 

 centre of the cavity of the beaks ; cavity of the shell rather deep and rounded ; cavity 

 of the beaks rather shallow and subangular ; nacre dark purple and iridescent. 



Soft Parts. — Branchial uterus situated on the posterior half of the outer branchise 

 where the branchial ovisacks are large and colored on the lower edges. Branchial 

 rather small, rounded below, the inner ones being much the larger, free only at the 

 point of the abdominal sack. Palpi rather small, oval, thin, united only at the upper 

 part of the posterior edges. Mantle rather thin, with a broad thick margin, the edges 

 being purplish, below the branchial opening furnished with numerous dark brown or 

 purplish papillse. Branchial opening small, with very small brownish papilla on the 

 inner edges. Anal opening very small, with numerous very minute papillce on the 

 inner edges. 'Super-anal opening small, united below for some distance, dark purple 

 or brown on the inside and outside of the edges. Color of the mass whitish, inclining 

 to salmon color. 



Embryonic sliell clear white and pouch-shape, and very near to obtusus (nobis) in 

 outline. 



Nearly all the branchial ovisacks were discharged, there being but few remaining 

 on each side. The attachment of the branchiae to the abdominal sack was not found to 

 be alike on both sides, owing, perhaps to some injury, or malformation. The small 

 opening mentioned above is on the right side, there being none on the left. 



Remarks. — Only two of this species were received from Bishop Elliott. It is 

 between glans (nobis) and concestator (nobis) in many of its characters. It has the 

 deep purple of glans and is a little larger, but differs in the epidermis being more 

 shining, browner and in having rays. It is much smaller than concestator, and by no 



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