6 DR. NELSON ANNANDALE ON 



P. pesmei. Srakao (Fisch. & Dautz.); Koh Samesan off 

 C. Liant. 



I have examined shells of all these species, and radulae of 

 P. conica, P. angelica, P. turbinis var. subampullacea, P. beg i at 

 and P. pesmei. 



Key to the Siamese species of Pachylabba 



I. Shell with 6£ whorls. 



A. Shell of moderate size, of very regular 

 ovoid form, with the mouth projecting 

 very 'little laterally ; the surface highly 



polished ... ... ... ... P. polita- 



B. Shell large, globose, with mouth 

 projecting abruptly from the body- 

 whorl ; the surface not highly polished P. angelica 



II. Shell with 4^ — 5J whorls. 



A. Shell somewhat elongate, of rather 

 small size, with the upper end of the 

 mouth considerably below the upper 

 margin of the body- whorl. 



i. Mouth of shell more than twice as 

 high as broad ; dark spiral bands 

 well developed ... ... ... ... P. gracilis. 



ii. Mouth of shell not more than twice 

 as high as broad ; dark spiral bands 

 obsolete or absent ... ... ... P. conica. 



B. Shell globose, with the spire little exserted 

 and the upper end of the mouth only 

 a short distance below the upper margin 

 of the body-whorl. 



i. Adult shell at least 70 mm. high, 

 never very thick, without a raised 

 and thickened peristome .-.. ... P. turbinis. 



ii. Adult shell between 50 and 60 ram. 

 high, very thick, with a raised' and 

 thickened peristome ...■* ... ... P. begini- 



JOURN. NAT. HIST. SOC. SIAM. 



