PSEUDODON I 08 I 



Section Suborbiculus Simpson, 1900. 



Suhorhiculus Simpson^ Syn., 1900, p. 835. 



Shell compressed, nearly round in outline, feebly biangulate, 

 and having a posterior dorsal wing ; beaks low ; hinge with a 

 single, compressed, smooth, slightly curved, triangular tooth 

 in each valve. 



Type, Monocondylns orbicularis Morelet. 



PsEUDODON oKBicui^ARis (Morelet). 



Shell suborbicular, compressed, thin, inequilateral ; beaks 

 small, acute, compressed, having in front of them a well- 

 marked, deep lunule; dorsal outline behind the beaks decid- 

 edly curved and rising to a wing ; behind this the dorsal slope 

 is subtruncate ; anterior end somewhat narrowed, rounded, 

 angled above at its junction with the lunule; base line well 

 curved ; posterior ridge somewhat double and feebly biangu- 

 late behind, the longer point of the biangulation being below 

 the median line ; surface with light, concentric sculpture, which 

 is more strongly developed at the border; epidermis brown- 

 ish, subshining; each valve has a single, compressed, elevated 

 and triangular, smooth tooth ; nacre bluish, pale salmon in the 

 cavities, iridescent. 



Length 74, height 60, diam. 22 mm. 



Siam ; Cambodia. 

 Monocondylns orbicularis M0RE1.ET, Rev. et Mag., XVIII, 



1866, p. 167. 

 Pseudodon orbicularis Morki,et. Ser. Conch., IV, 1875, p. 



338, pi, xvT, fig. 5. — Simpson, Syn., 1900. p. 835. 

 Monocondylcea orbicularis P^tel, Conch. Sam., Ill, p. 174. 



Evidently a fine species. The outline is suborbicular, the 

 length being slightly greater than the height. There is a deep 

 lunule, which cuts into the outline of the shell and below it the 

 anterior end is strongly angled. The species cannot be mis- 

 taken for any other. 



Section Trigonodon Conrad, 1865. 



Trigonodon Conrad, Am. Jl. Conch., I, 1865, p. 233. 



Shell solid, compressed rhomboid, round in front, widely 

 and faintly biangulate and rough behind ; surface irregularly, 



