1096 PSKl'DOnON 



is a low, radial ridge on the posterior slope midway between 

 the upper part of the posterior ridge and the dorsal line, that 

 ends in a slight angle behind ; hinge with a strong, very prom- 

 inent, triangular tooth in each valve ; anterior muscle scars 

 well marked ; posterior scars shallow ; dorsal scars six in each 

 valve, forming a row under each beak, deep ; nacre grayish- 

 white. 



Length 84, height 48, diam. 38 mm. 



Cambodia ; Siam. 

 Pscudodus chaperi de Morgan, Bull. Soc. Zool. de Fr., X, 



1885, p. 423, pi. IX, figs. T, 2. 

 Pseiidodon ciiaperi Simpson, Syn., 1900, p. 838. 



de Morgan places this species and the Anodonta ciimingii 

 Lea in the genus Pseudodjts and credits the genus to Gould, 

 who bestowed the name Pseiidodon on the group of oriental 

 Naiades having a single large tooth in each valve and practi- 

 cally wanting laterals. The author of this species describes it 

 as having very long laterals, but they probably are rudiment- 

 ary, as the shell seems to be a Pseiidodon. Its distinguishing 

 characters are its strong, concentric sculpture and the decided- 

 ly wide, double posterior ridge. 



PsEUDonoN WAT.Poi.Er (Hanley). 



Shell irregularly rhomboid, considerably narrowed in front, 

 convex, rather solid, inequilateral ; beaks moderately elevated, 

 not inflated; posterior ridge full, rounded, ending in a blunt 

 point at the base of the shell ; above it there are two or more 

 faint, radial ridges, the middle part of the dorsal slope is ir- 

 regularly and strongly plicate ; anterior end narrowed and 

 rounded, subangulate above ; base line straight or lightly ar- 

 cuate ; hinge line curved a little ; outline of dorsal slope ob- 

 liquely rounded, angled behind the ligament ; teeth single in 

 each valve, smiall and but .little elevated ; dorsal scars few, 

 placed in a row under the beaks ; muscle scars shallow ; nacre 

 lurid purplish ; ligamental sinus well marked. 



Length 55, height 32. diam. 19 mm. 



Borneo. 

 Monocondyloca walpolei Hanlky, Proc. Zool. Soc. Lond., 1871,. 



p. 587. — SiiNiPSOx, Syn., 1900, p. 840. 



