II02 PSEUDODON 



curved, almost horizontal ventral margin. Posterior end 

 nearly peq)endicular ; posterior slope curved ; posterior dorsal 

 margin at first straight, then rather sharply curved where it 

 joins the posterior margin. Beaks situated at 21-100 of the 

 total length, quite swollen, extending slightly above the pos- 

 terior dorsal margin and very much above the anterior dorsal 

 margin, eroded, showing, however, remnants of a scul])ture 

 consisting of close, concentric ridges. Posterior slope quite 

 high, somewhat compressed, posterior ridge indistinct. Areola 

 small, ligament long, strong, half-icovered. Simulus broad 

 lanceolate, cutting deep into the beaks. Sinus not recogniza- 

 ble. Epidermis brownish-black, lighter towards the beaks. 

 Outline from above narrow lanceolate, decreasing quite regu- 

 larly in thickness from front to rear. Hinge with two, blunt, 

 tooth-like projections, that in the right valve obtusely trian- 

 gular, quite high and stands in front of the beak, while that of 

 the left valve is longer and is situated under the beak. An- 

 terior muscular impressions deep, confluent, (that of the lower 

 retractor is very large almost separated), the posterior im- 

 pressions are shallow and confluent. The dorsal muscular 

 impressions. 4-6, lie in a groove in the beak cavity. Nacre 

 porcellaneous, bluish-white, slightly iridescent. 



Length 92, greatest height 54, at beaks 45, diam. 31.5 mm." 

 (Plaas). 



Type locality, Hunan, Central China. 

 Pseudodon solidus Haas, Nachr. Deutsch. Mai. Ges., 191 1, p, 



46. 



Pseudodon ponderosus Preston. 



''Shell solid, moderately convex, sub-trapezoidal, covered 

 with a coarse, black, scaly periostracum, which becomes lamin- 

 if erous towards the posterior side ; anterior side bluntly round- 

 ed ; posterior side rounded above, somewhat rostrate below ; 

 dorsal margin slightly arched ; ventral margin almost straight ; 

 unibones large, prominent ; interior of shell nacreous, irides- 

 cent, tinged with pinkish mauve, deepening posteriorly. 



Length 117, height 66 mm." (Preston). 



Type locality, Nan-ko, Siam. 



