DIPLODON 



1255 



DiPLODON DEMERARAKNSis (Lea). 



Shell rhomboid oblong, inequilateral, convex, rather solid ; 

 beaks moderately full, sculptured with radial bars ; surface 

 strongly concentrically sulcate ; epideniiis olive-brown, rayless ; 

 pseudocardinals subcompressed striate, erect, double in both 

 valves; laterals somewhat curved; nacre white and iridescent. 



Length 38, height 23, diam. 13 mm. 



Demerara. 

 Unio demararaensis Lea, Pr. Ac. N. Sci. Phila., XL 1859, p. 



152. 

 Unio demeraraensis Lea, jl. Ac. N. Sci. Phila., IV, i860, p. 



253, pi. XXXIX, fig. 133 : Obs., Vn, i860, p. 71, pi. xxxix, 



fig- ^33- — Rkeve, Conch. Icon., XVI, 1865, pi. xxii, fig. 99. 

 Margaron (Unio) demeraraensis Lea, Syn., 1870, p. 36. 

 Diplodon demararaensis Simpson, Syn., 1900, p. 880. 

 Unio demarasensis P.^Tei,, Conch. Sam., Ill, 1890, p. 150. 



I have never seen this shell ; the type, which is the only 

 specimen known, being in the Cumingian collection. Were 

 it not that Dr. Lea distinctly states that it has radial beak sculp- 

 ture of the South American type, I should be sure that it was 

 a young Unio dysoni, which species is figured beside it in the 

 Observations. The form, the slight biangulation behind, the 

 strong sulcation and the character of the teeth would seem to 

 place it with or close to Nephronaias dysoni. I am not at all 

 sure that it should not be made the type of a separate group. 

 By an error this was written demararaensis in the Synopsis. 



Diplodon lepidior (Lea). 



Shell oblong, somewhat rhomboid, scarcely subsolid, convex, 

 inequilateral ; beaks not very full, rising a little above the dor- 

 sal line, their sculpture a number of rather strong, straight, 

 radial ridges, the middle ones converging a little below ; pos- 

 terior ridge low, rounded, with a feeble radial rib above it ; 

 surface with close, fine growth lines ; epidermis yellowish- 

 green, the hinder half of the shell darker and there is some- 

 times a broad, dark, concentric, central band, the whole smooth 

 and shining ; the two pseudocardinals of the left valve are com- 



