PRISODON 



Prisodon alatus (Sowerby). 



Shell irregularly triangular, somewhat inflated, slightly ine- 

 quilateral ; dorsal outline strongly incurved, carried out into a 

 narrow elongated wing in front and into a wide, much pro- 

 duced, upcurved wing behind ; beaks low and not much swollen ; 

 posterior ridge apparently angled, but slightly elevated, ending 

 in a widely rounded projection at some distance above the base ; 

 base much rounded; anterior end narrowed, cut away and 

 rounded below, its outline sinuous ; posterior end greatly in- 

 curved in the middle; surface nearly smooth, olive-brown. 



Length from tip to tip of wings 115, from tip of front wing 

 to post-basal point 115, extreme height 85 mm. 



Guiana. 

 Hyria data Sowerry, Conch. Icon., XVIT, 1869, pi. v. fig. 13. 

 Prisodon alatns Simpson, Syn., 1900, p. 871. 



A form, which seems to have had a most rampant develop- 

 ment. The wings are excessively produced, the outlines below 

 them are greatly incurved. The base line is rounded; the 

 lower posterior part of the shell is likewise rounded. 



Prisodon castklnaudi (Hupe). 



Shell large, triangular, convex or subinflated, inequilateral, 

 quite solid ; beaks rather full and high ; posterior ridge rounded, 

 having a blunt, rounded termination near the base; base Hue 

 elongated, very slightly curved; anterior end greatly narrowed, 

 rather sharply winged; dorsal outline nearly straight, being 

 produced into a wing behind the beaks ; dorsal slope obliquely 

 truncate, shorter than the dorsum ; surface rather strongly, 

 concentrically wrinkled; epidermis yellowish-green; pseudo- 

 cardinals somewhat compressed, and, with the laterals, verti- 

 cally striate ; nacre white, bluish or iridescent on the border. 



Length 143. height 90, diam. 45 mm. 



Brazil. 

 Hyria castelnandi Hite, Moll. Nouv.. TIL 1857. p. 81, pi. xvi, 



fig. I. — Sowerby, Conch. Icon.. XVIT, 1869. pi. iv, fig. 8. 

 Prisodon castelnandi Simpson, Syn., 1900, p. 871. 



This may be only a form of ohliquns, but its outline is almost 

 triangular, the base forming the longest side, the dorsiun, the 



