PHYSUNIO. PSEUDODOX. 149 



Range. Slain ; Cambodia ; Assam. 



Shell sublenticular ; three laterals of left valve distinct ; cavity 

 of the beaks compressed. 



284. Physunio (Lens) velaris (Sowerby). 



Physunio (Lens) velaris (Sowerby) ; Simpson, Washington, D.C., 

 Smiths. Inst, Nat. Mus. Proc. xxii, 1900, p. 831. 



Unto velaris, Sowerby, Conch. Icon, xvi, 1868, pi. 72, fig. 368 ; 

 Psetel, Conch. Sam. iii. 1890, p. 171 ; Benson in Hanley, Rec. 

 Biv. Shells, p. 385, pi. 23, fig. 42. 



Original description : Shell small, thin, rather compressed, pale 

 green, neither radiated nor sculptured ; anterior extremity very 

 narrow; posterior side winged, ventral margin arcuated, rising 

 abruptly anteriorwards, beaks very acute, prominent, lunule exca- 

 vated ; nacre white ; cardinal teeth large, lamellar, approximate. 



The following note is appended to Sowerby's description : 



"The abrupt fall of the front dorsal margin in this symphonote 

 species give a seeming projection to the beaks. Both dorsal edges 

 are angulated above, and rounded off below ; the hinder dorsal 

 edge is much elevated. The compression of the valves is espe- 

 cially conspicuous on the anterior portion of the shell." 



As the author gives no dimensions the following are taken from 

 the figure in the k Conch. Icon/ 



Long. 55, lat. 59 '5 mm. 



Hub. Assam. 



Genus PSEUDODON. 

 Pseudodon, Gould, Proc. Boston Soc. Nat. Hist, i, 1844, p. 161. 



TYPE, Anodonta inoscularis, Gould, from the Salwen Eiver, 

 Burma. 



Range. Siain and Indo-China ; Burma; China; Java; Sumatra; 

 Borneo ; Malacca ; Nicobars ; Japan. 



Hinge margin with a tooth-like apophysis on each valve, the 

 surface of which is not fractured, but smoothly covered with 

 enamel, fitting into corresponding undulations in the opposite 

 valve, that on the right valve closing in front of that on the left. 



Section TRIGONODON. 



Trigonodon, Conrad, Proc. Boston Soc. Nat. Hist, i, 1865, 

 p. 233. 



TYPE, Monocondylcea peyuensis, Anthony, var. crebristriata, 

 Anthony; Pegu. 



Range. Burma; Cambodia. 



Oval, somewhat compressed, with a prominent triangular 

 cardinal tooth in each valve, with a deep pit behind it for the 

 reception of the tooth of the opposite valve. 



