THE APPLE-SNAILS OF SlAM. 



Height of mouth (oblique) 



Maximum diameter of mouth 



Maximum diameter to height 



Maximum diameter to heigh tof 

 mouth 



Mouth to height 



Max. diam. mouth to max. diam. ., 



These shells are all from Cambodia. Kobelt states that 

 P. polita is the characteristic form of that country and of Cochin 

 China. It is probably less common in Siam than the forms of 

 P. turbinis, but has been recorded from Bangkok and Chiengmai. 



Pachylabra conica (Gray). 



1911. Pachylabra conica, Kobelt, oj). cit., p. 93, pi. si, figs. 1-5, 8. 9. 



In some respects the shell of this species resembles that of 

 P. polita, but it is usually smaller and never has the same regular 

 ovoid shape, highly polished surface or finished appearance. The 

 mouth projects abruptly in ventral view and the whorls are more 

 tumid, the suture more regularly oblique. The sculpture of the 

 surface is also different, the longitudinal striae being much coarser 

 and more irregular, fine longitudinal ridges being often present on 

 the body-whorl and spiral, minutely interrupted lines also occur- 

 ring in large numbers. The mouth is as a rule broader and more 

 oblique and the spire blunter. 



The colour is dull olivaceous green or brown, occasionally 

 with irregular longitudinal dark lines and usually with obsolete 

 brownish spiral bands. The lip is very narrowly, if at all, blackened. 

 The interior of the shell is ornamented with fairly conspicuous 

 brownish spiral bands, which sometimes extend to the periphery of 

 the lip, which is sometimes white. 



The operculum is relatively broader and shorter than that of 

 P. polita, with a rather more regular ovoid outline. The inner 

 border of the muscular scar is sometimes rather deeply sculptured 

 in a concentric manner, as is shown in Kobelt's figure, but this is 

 not a constant character. 



The radula closely resembles that of other species of 



VOL. IV, NO. !, 1920. 



