16 DR. NELSON ANNANDALE ON 



aperture very large, elongately ovate, brownish and much 

 banded within ; outer lip acute ; columella very much incurv- 

 ed and thickened ". 



"Diam. 2.36, Length 2.46 inches". 



Several local races are found in different parts of Siam and 

 the adjacent countries and it is improbable that all the references 

 given above refer to the forma typical. It will be well, therefore, 

 to give a new description of this form. 



The shell is large, globose, of moderate thickness. There 

 are 4^ whorls but the apex is often eaten away. The total height 

 is the same as, or practically the same as, the maximum diameter. 

 The spire is depressed and flattened at the base. It j>rojects very 

 little, but is somewhat variable in its exact proportions. The 

 upper surface of all the whorls is slightly flattened, but they are 

 never augulate or carinate. The suture is moderately impressed. 

 The body-whorl is very broad and not very oblique. The mouth of 

 the shell is large and nearly or quite twice as high as broad. Its 

 upper extremity is separated from that of the body-whorl by a 

 distance distinctly greater than the length of the spire. The 

 umbilicus is very narrow and is more or less completely concealed by 

 the expanded columellar callus. In shells that have finished their 

 growth-period the callus is well developed and thick but not promi- 

 nent. There is a low, narrow rather indistinct thickening of the 

 shell inside the lip, which is sharp. This thickening is most 

 strongly developed in the upper angle. The lower extremity of 

 the mouth is very little everted. 



The surface of the shell has a smooth and polished but not 

 brilliant appearance. The sculpture is much like that of P. angelica 

 but more irregular and with the thicker longitudinal ridges coarser 

 and the transverse striae less well developed. 



The colouration of the shell is variable. Young specimens 

 are spirally banded and the bands may persist to some extent in the 

 adult or subadult. One of the shells assigned by Nevill to his var. sub- 

 globosa has traces of them. In fully adult shells there are narrow 

 longitudinal dark lines, sometimes set at very regular intervals. 



JOURX. XAT. HIST. SOC. SIAM. 



