pse:udodon ■ 109 1 



"Nearest to Ps. aeneolns Drouet from Borneo, but propor- 

 tionately longer and with more strongly impressed sculpture. 

 These two Pseudodons are, to my knowledge, the only ones 

 with the folds bent upwards on the posterior surface and al- 

 most deserve to be put in a small group, resembling the genus 

 Ptychorhyncus Simp., in which Unio apiceilatus Heude in- 

 vites comparison, but they have no indications of lateral teeth, 

 only a stout, somewhat swollen hinge margin as in M. mar- 

 garitifera L. ; whereas both in Simpson's generic diagnosis 

 and in Heude's figures the usual lateral teeth of Unio clearly 

 appear ; to be sure, Heude says of many of his species that they 

 properly belong to Alasmodonta, but this is in contradiction of 

 his figures. 



The intensity of the sculpture seems to be variable ; on one 

 mature example, in addition to the upward curved folds on 

 the hinder part, there are in the middle a few almost vertical 

 wrinkles, slightly curved forwards, that are wholly wanting 

 in others ; on two somewhat smaller specimens which, how- 

 ever, can not be considered as young, the characteristic up- 

 ward curved folds are as feeble as in Heude's figure of 

 apiceilatus, but they are decidedly stronger on the example 

 on which I base my description. On one specimen I count 

 but two, on another four small, rounded muscular impres- 

 sions." 



PSEUDODON TUMIDUS (Morclct). 



Shell nearly elliptical, inilated. rather thin, inequilateral; 

 beaks full and elevated ; dorsal outline generally rounded, hav- 

 ing a deeply impressed lunule in front and a slight prominence 

 just at the end of the ligament ; anterior end somewhat nar- 

 rowed, rounded ; base line evenly curved, not quite so full as 

 the dorsal outline; posterior ridge high, narrowly rounded, 

 ending in a blunt point just below the median line ; epidermis 

 yellowish-brown in young shells, chestnut in adults ; teeth sin- 

 gle in each valve, rather strong, smooth ; nacre bluish-white, 

 fulvous under the beaks. 



Length 70, height 46, diam. 34 mm. 



Siam ; Cambodia. 



