THE APPLE-SNAILS OF SIAM. 23 



from 1J to twice as high as broad. The total height is fromli to 

 If that of the mouth and the maximum diameter is about twice 

 that of the mouth. 



The species is said to be common on the lower Mekong and 

 in Cambodia. Mr. Boden Kloss found it abundant in rice-fields at 

 Lat Bua Kao near Korat. 



Pachylabra pesmei (Morlet). 



1889. Avipidlaria pesmei, Morlet, op. cit, p. 185 pi. viii, fig. 2. 

 1904. Ampullaria pesmei, id., op', cit., p. 369, pi. xx, fig. 12. 

 1911. Pachylabra pesmei, Kobelt, op. cit., p. 88, pi. xxxv, fig. 8. 



P. pes7nei is one of the smallest species in the genus. It 

 has a thinner shell than P. begin i, to which it is closely related, 

 and the peristome, though complete, has not the same prominent 

 character. The umbilicus also is much narrower. The colour of 

 the shell varies. In Morlet's type it had a curious bluish pink 

 tinge. In the shells I have seen it is rather pale olivaceous brown 

 with or without rather faint spiral bands externally. The interior 

 of the shell is yellowish with a tinge of purple and marked with 

 dark purple spiral bands, which are sometimes confluent and become 

 more conspicuous on the interior of the lip. The peristome is yel- 

 lowish. The external surface has a rather high polish and the 

 sculpture resembles that of the shell of P. begini but is finer. 



The operculum is thinner and more pointed posteriorly than 

 that of P. begini, and the sculpture of the border of the scar has on 

 the inner margin of the smooth area a concentric arrangement. 



The radular teeth are relatively large. The central is more 

 than three times as broad as high and the cusps of all the teeth are 

 narrower in proportion than in P. begini. 



Measurements (in millimetres) and Proportions of shells. 



Height 32 30 31 32 31 



Maximum diameter 30 27 28 29 28 



Height of mouth 24 21 23.5 23 23 

 Maximum diameter of 



mouth 15 12 11 13 12 



VOL. IV. NO. 1, 1920. 



