niYSUXIO. — PSEUDODOX. 141) 



liange. Siam ; Cambodia ; Assam. 



Shell sublenticular ; three laterals of left valve distinct ; cavity 

 of the beaks compressed. 



284. Pliysimio (Lens) velaris {Sowerhy). 



Pltysunio {Lens) velaris (Sowerby) ; Simpson, Washington, B.C., 

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



T'liio velaris, Sowerby, Concli. Icon, xvi, 1868, pi. 72, fig. 308 ; 

 Pa3tel, Conch. Sam. iii. 1890, p. 171 ; Benson in Ilanley, Rec. 

 J5iv. SheUs, p. 385, pi. 23, fig.'42. 



Original description : — Shell small, tliin, rather compressed, pale 

 green, neither radiated nor sculptured ; anterior extremity very 

 narrow ; posterior side winged, ventral margin arcuated, rising 

 abruptly anteriorwards, l)eaks 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 tbis symplionote 

 species give a seeming projection to tlie beaks. Botb dorsal edges 

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

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

 cially conspicuous on the anterior portion of tlie sbell." 



As the author gives no dimensions the following are taken from 

 the figure in the 'Conch. Icon.' 



Long. 55, lat. 59-5 mm. 



Hah. Assam. 



Genus PSEUDODON. 

 Pseudodon, Gould, I'roc. Boston Soc. Xat. Hist, i, 1814, p. 161. 



Type, Anodonta i)ioscularis, Gould, from the Salwen Eiver, 

 Burma. 



liange. Siam and iudo-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 cori-esponding undulations in the opposite 

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



Section TEIGONODO^\ 



Trigonodon, Conrad, Proc. Boston Soc. Nat. Hist, i, 1805, 

 ,. .100 



p. -'JO. 



Type, Jlonocondghm jf'^gii'Cnsis, Anthony, var. crchristriata., 

 Anthony ; Pegu. 



Range. Burma; Cau)bodia. 



Oval, somewhat compressed, \\ith a prominent triangular 

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

 reception of the tooth of the opposite valve. 



