56 NEW UNIONID.?': OF THE 



to gamboge yellow. My smallest specimen is about au inch wide, and 1 doubt if the 

 yellow iiacre exist in those much younger. The outline is quadrate, varying towards 

 rotund, the younger being very nearly round. The epidermis in old fine specimens is 

 almost jet black ; in the younger it is very dark green and obscurely rayed. Usually 

 in the full grown there are eight oblique folds between the beaks and the basal margin, 

 the four or five last being large and occupying nearly the whole space. There are 

 usually four small nearly concentric undulations at the tip. The interior border in 

 good specimens has a well marked black line more developed on the posterior portion. 



Unio gracillior. pi. 8, fig. 38. 



Testa lasvi, elliptica, inflata., iuEequilaterali, valvulis tenuibus ; natibus prominulis; epidermide tenebroso- 

 fusca, obsolete radiata et nitida ; dentibus cardinalibus compressis erectisque ; lateralibus laniellatis, 

 longis subcurvisque ; margarita albida et valdfi iridescente. 



Shell smooth, elliptical, inflated, inequilateral ; valves thin ; beaks a little promi- 

 nent; epidermis dark brown, obscurely radiated and bright; cardinal teeth compressed 

 and erect ; lateral teeth lamellar, long and somewhat curved ; nacre whitish and 

 very iridescent. 



Proc. Acad. Nat. Sci., 185G, p. 262. 



Bah. — Buckhead Creek, Georgia, and Tobesaufke Creek, near Macon, Georgia. 

 Bishop Elliott. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. -6, Length 1-1, Breadth 2 inches. 



Shell smooth, elliptical, inflated, inequilateral, rounded behind and before ; sub- 

 stance of the shell thin, slightly thicker before; beaks slightly pi*ominent; lines 

 of growth few and rather distant; ligament somewhat long and slender; epidermis 

 dark brown, shining, transversely wrinkled, obsoletely radiate; umbonial slope rounded; 

 cardinal teeth rather small, oblique, compressed, erect and slightly crenulate, single 

 in the right and double in the left valve ; lateral teeth long, lamellar, slightly curved, 

 single in the right and double in the left" valve ; anterior cicatrices distinct ; posterior 

 cicatrices confluent ; dorsal cicatrices small and placed nearly in the centre of the 

 cavity of the beaks; cavity of the shell rather deep; cavity of the beaks rather shal- 

 low and subangular ; nacre bluish-white and very iridescent. 



Soft Paris. — Branchial uterus situated on the posterior half only, of the outer bran- 

 chiae, and in the specimen before me presenting sixteen branchial ovisacks'" in each 

 of the outer branchiae. These extend a short distance beyond the edge of the 

 branchige. Branchice rather large, inner ones much the larger and nearly round 

 balow, free only at the point of abdominal sack. Falpi rather large and subtrian- 



*This term is applied to the individual sack, situated within or attached to the branchiae, the whole number 

 in the aggregate being considered as the brrinchial vtrrnn. 



