THE APPLE-SNAILS OF SIAM. 13 



epidermis is moderately thick and not highly polished ; it is of a deep 

 brownish colour. The nacre is livid greyish stained with pink. The 

 muscular scar is large, its smooth area is long, narrow and prominent. 

 The sculptured border is broad and shallow except at the outer 

 anterior extremity, where there is a distinct pit. The sculpture of 

 this border is obscure and shallow. 



The exposed parts of the animal are of an almost uniform 

 sooty black colour. The foot is large, narrowly cordate and bluntly 

 pointed behind. The tentacles are long and slender and the oral 

 processes taper distinctly to their extremity, which is filiform. The 

 siphon is short and broad. 



The jaws are stout and strongly chitinizjd ; each has a single 

 projection on its free edge. The radular teeth are also strongly 

 chitinized. They have the usual formula (2. 1. 1. 1. 2.) and closely 

 resemble those of P. conica except that they are larger and stouter, 

 with broader denticulations. The central is 2±- times as broad as 

 high, and the latero-basal folds on its disk are very poorly develop- 

 ed. The distal part of the marginals is longer and stouter, and 

 the outer denticulations of the outermost tooth is much smaller 

 than the middle one. The most noteworthy radular character is the 

 large size of the teeth. 



Measurements (in millimetres) and Proportions of Shells. 



Height 75 73 - 65 



Maximum diameter 65 66 60 



Height of mouth (oblique) 58 55 51 

 Maximum diameter 



_ of mouth 31 31 27 

 Maximum diameter 



to height 1:1.15 1:1.1 1:108 

 Maximum diameter 



to height of mouth 1:1.87 1:1.77 1:1.9 



Mouth to total height 1:1.29 1:1.32 1:1.27 

 Max. diam. mouth to total 



max. diam. 1:2.09 1:2.12 1:2.22 



The width of the shell is thus slightly less than the height, 



VOL. IV, NO. 1, 1920. 



