268 Records of the Indian Muscuin. [Voi,. XXII, 



outer margin. The umbilicus is narrowly perforate or completely 

 closed, rarely more open, the columella is strom^ly arched, with a 

 narrow margin and b}^ no means prominent, the outer lip is almost 

 semicircular, sharp, thin and joined to the columellar margin above 

 as a rule merely by a thin, glary deposit In the adult shell the 

 sculpture consists of fine longitudinal ridges, which are convex 

 outwards and on the body- whorl sometimes take the form of fine 

 irregular ribs or varices. Only traces of spiral sculpture can as a 

 rule be distinguished on adult shells, but the young shell bears 

 rows of very fine punctae, representing the bases of minute chaetae. 

 The colouration varies considerably, but is alwa3's some shade of 

 greenish- olivaceous, marked with dark spiral bands. These are as 

 a rule narrow, but broader bands alternate with still narrower, 

 often paler linear ones of the nature of ' shadow stripes. ' The bands 

 are occasionally rendered obsolescent, though rarely or never 

 quite obsolete, either bj' a general deposit of dark pigment or by 

 an incomplete albinism. The fully develo'.ied mouth usually has 

 a narrow black rim. 



The operculum is moderately thin and of a deep brownish 

 colour. The external surface is concnve as a whole. The outer 

 margin is strongly curved, the inner margin slightly sinuate and the 

 posterior extremity blunth' pointed. The muscular scar is moder- 

 ately large and prominent, much deeper in colour than the rest of 

 the operculum. 



In all races two types of shell can be found. They may be 

 called the normal type and the elongate. In the former the shell 

 is considerabh' more globose, broader in proportion to its height, 

 with a larger mouth and a shorter spire than in the other. The 

 difference is not sexual, but apparently dimorphic. In most races 

 the normal type is much the commoner, but in the phase annan- 

 dalei the proportionate numbers of the two are reversed, and this 

 is also so in the race baUcata. In the race colnirensis the normal 

 type is about as elongate as the elongate type in the forma lypica, 

 but shells of a still more eloirgate type are also found occasionally. 



In the forma iypica and in the race mandiensis a third type 

 of shell is sometimes found. It may be called the gigantic type, 

 for its characters are great size, more swollen whorls, broader 

 umbilicus and more projecting mouth. Sometimes, especially in 

 large marshes, this type shows a tendency to predominate and 

 almost assumes the rank of a phase. 



Yet a fourth type occurs, much more rarely than the others, 

 namely^ the canaliculate, in which the outline is extremely broad 

 and the surface outside the suture deeply impressed. »Single shells 

 of this type have been found in the forma iypica and in the dark 

 form of the race eburnea. 



The elongate type of shell was called PaUtdina elongata by 

 Swainson, the gigantic P. gigantica by Reeve and the canaliculate 

 P. bengalensis var. canaliculata by Nevill, but I have avoided the 

 use of these latinized names, for as a rule they apparently 

 represent mere aberrations. 



