10 DR NELSON ANNANDALE ON 



Pachylabra, a genus in which .specific differences are not strongly 

 marked in the teeth. Each transverse row consists of seven teeth, 

 two marginals and one lateral on each side of an unpaired 

 central, giving the dental formula 2. 1. 1. 1. 2. The central 

 is transverse and about twice as broad as high. It bears at either 

 side of its base a fairy prominent almost vertical fold and its free 

 margin is armed with five denticulations, all of which are sharply 

 pointed, while the central denticulation is much larger than the 

 others and extends downwards nearly to the base of the tooth. 

 The lateral is comparatively stout, and its free margin resembles 

 that of the central. The marginals have their inner margin dis- 

 tinctly S-shaped. They each bear three long, pointed denticulations, 

 which in the outermost tooth are subequal. The teeth are all com- 

 paratively small. 



Measurements (in millimetres) and Proportions 

 of Shells. 



Height ... 24 



Maximum diameter ... 35 

 Height of mouth ... 30 



Maximum diameter of 



mouth ... 17 15 17 14 14 14 



Maximum diameter to 



height ...1:1.2 1:1.2 1:1.2 1:1.17 1:1.25 1:1.07 



Mouth to height ... 1 : 1.2 1 : 1.37 1 : 1.51 1 : 1.46 1 : 1.56 1 : 1.28 



Maximum diameter to 



height of mouth ... 1:1.76 1:2 1:1.59 1:1.71 1:1.64 1:1.64 



Maximum diameter of 



mouth to that of shell ... 1 : 2.05 1: 2: 44 1:2 1 : 2.14 1:2 1 : 2.28 



The average proportion of maximum diameter to height of 

 shell is, therefore, in this series 1 : 1.18, or considerably more than 

 £ ; the average proportion of the height of the mouth to the height 

 of the shell 1 : 1.43 ; that of the maximum diameter of the mouth 

 to its height 1 : 1.72, considerably more than one half; that of the 

 width of the mouth to the total width slightly less than half. 



The series of shells of which these measurements are given is 

 from Akyab in Arakan. The species is the dominant one in LoAver 



JOUKN. NAT. HIST. SOC. SIAM. 



