THE APPLE-SNAILS OF SIAM. 19 



thicker than that of the forma typica. The spiral bands are less 

 obsolete, especially on the internal surface, than in either, the lip is 

 paler in colour than in the latter and there is a more definite thick- 

 ening just inside its margin. 



The operculm is rather thin and the smooth area of the 

 scar is relatively large. 



The radula is normal. The teeth aL'e large. The central 

 tooth is rather more than 2\ times as broad as high. Its lower 

 angles are produced and sharp, the folds on its disk triangular and 

 prominent ; the central denticulation does not reach the base of the 

 tooth and has only two well-developed smaller denticulations on 

 each side. The other teeth are broad at the base. The lateral has 

 the central denticulation as broad at the base as long and two small 

 denticulations at either side, The denticulations of the marginals 

 are long, sharp and unequal. 



Measurements (in millimetres) and Proportions of Shells. 



diameter, the height of the mouth about twice its maximum diame- 

 ter. The height of the shell is about 1£ the height of the mouth 

 and its maximum diameter 1^ to a little over 11 the maximum 

 diameter of the mouth. 

 Type-specimen. No. 2427 M ( Z. 8. I. ). 



This is evidently the Malayan race of the species, but its range 

 extends northwards into Peninsular Siam. It was originally des- 

 cribed from Perak, is stated by Mollendorf to be common in the Malay 



VOL. IV, NO. 1. 1920, 



