98 Records of the Indian Museum. [Vol. XXIV, 



the species peguensis with its two varieties must now be separated 

 from it. The arrangement, however, is only provisional till the 

 soft parts of these forms are investigated. 



Trigonodon peguensis (Anthony). 



1900. Psendodon crebristriatus var. peguensis, Simpson, op. cit. p., 



8 35- . " . 



1 914. Pseudodon peguensis, Simpson, op. at., pp. 1083, 1084. 



1915. Pseudodon peguensis, Preston, op. cit., p. 150. 



As stated in the notes on the genus above, I have been obliged 

 to revive Conrad's generic name Trigonodon for this species and its 

 varieties. The type-species of the genus is M onocondylaea crebri- 

 striatus Anthony, which I think is no more than a variety of T. pegu- 

 ensis. 



Simpson in his first work treated this species as a variety of 

 M. crebristriatus, but in his Descriptive Catalogue he was doubtful 

 whether the two were distinct. His first course was not correct 

 since, if the two forms are varieties of the same species, the name 

 of the species should be T. peguensis, this being the first of the two 

 species described by Anthony. 



As a result of my examination of a fair series of specimens of 

 this species and of the form crebristriatus from Pegu I am 

 unable to consider the two as distinct species. The latter, how- 

 ever, owing to the shells being more compressed and the sculpture 

 more strongly marked, with the umbones a little more inflated, 

 may be regarded as a distinct variety. 



var. crebristriatus (Anthony). 



1914. Pseudodon crebristriatus, Simpson, op. cit., pp, 1082, 1083. 



1915. Pseudodon crebristriatus, Preston, op. cit., pp. 150, 151. 



There are only two specimens of this form in the Indian Muse- 

 um collection, from Pegu, the type-locality. They resemble the 

 original description very closely and only differ from typical T. 

 peguensis in the points already noted. 



var. curvata (Preston). 



1915. Pseudodon peguensis var. curvata, Preston, op. cit., p. 152, fig. 

 9 (1. 2, 3). 



This form, of which I have seen a large series from Pegu, 

 differs from the forma typica and the var. crebristriatus in having 

 a less ovate shape, distinctly curved ventral margin, hardly 

 projecting umbones and in having only very faint sculpture on 

 the posterior wing. 



Genus Indopseudodon, nov. 



I have very reluctantly adopted the course of introducing a 

 new generic name for the species P. salwenianus and P. ava, as the 

 anatomy of the related forms is not known and as so many new 



