I, A M KI^L I DK N S 1 1 6 5 



Genus LAMELLIDENS Simpson, 1900. 



Lamellidcns Simpson, Syn., 1900, p. 854. — Ortmann, Ann. 



Car. Mus., VIII, 1912, p. 277. 



Shell elongate, elliptical, pointed behind, with a sliglit post- 

 dorsal wing, a low, often biangulate, posterior ridge and gen- 

 erally two sharp, radiating lirae above it; beaks with curved, 

 radiating ridges, which sometimes are slightly zigzag, and 

 often become almost concentric, but which fade out as they 

 approach each other at the center of the disk ; epidermis smooth,^ 

 generally shining, brownish, often with concentric bands of 

 lighter color, rayless or nearly so ; left valve with two com- 

 pressed pseudocardinals, the front one roughened, and two 

 laterals ; right valve with two parallel, lamellar pseudocardinals 

 and one lateral ; cavity of the beaks rather shallow ; dorsal 

 scars few, deep, distinct, scattered; anterior scars separate; 

 nacre bluish-white to straw. 



Animal unknown. 



Type, Unio marginalis Lamarck. 



The genus Lamellidens contains a number of closely allied 

 species, which seem quite distinct from other Naiades of the 

 Oriental Region. The group appears to be closely alHed to the 

 subgenus HyridcUa of Diplodon so far as shell characters have 

 been observed. The beak sculpture consists of subradial 

 curved bars much like that of the Australian species, but they 

 sometimes are slightly zigzagged. The general texture and 

 color of the shells are something like those of the Australian 

 species, the epidermis being usually dark and always rayless. 



If I am correct in placing the Anodonta guillaini of Riecluz 

 in this group it will be seen that Lamellidens has a distribution 

 somewhat similar to that of Nodularia and Parreysia. 



Key to spkcies of I^amellidens. 



Shell with imperfect hinge teeth, L. guillaini. 



Shell with well developed hinge teeth. 

 With a moderately developed post-dorsal wing. 



Trapezoid, base slightly rounded, L. pulcher. 



Elliptical or obovate, base rounded. L. generosus- 



