Invertebrate Gallery of the Indian Museum. 125 



Observe the peculiar form of the shell of Magilus in Case 

 162B : Maorilus lives in crevices in growing coral-stocks, 

 and as the coral spreads, the Magilus^ in order to avoid 

 being overgrown and buried, continuously lengthens its 

 shell at the mouth, until at last the shell comes to be 

 nothing more than a long irregular tube, not unlike a large 

 worm-tube. 



13th Family, Mitridse [Cases 162C — 164B]. 



The species of this large family are almost exclusively 

 tropical, and are specially numerous in eastern seas. The 

 shells are very beautifully sculptured and coloured, and 

 have generally a long sharp spire. The inner lip of the 

 mouth of the shell is marked by several oblique folds and 

 ridges, and an operculum is either rudimentary or absent. 



14th Family, Olividae [Cases 164B — 165B]. 



The shells of the Olividse somewhat resemble those of 

 the Cypraeidas by reason of their polish and shape, the last 

 whorl, which is of great size, more or less completely 

 enclosing and concealing the spire. The inner lip of the 

 Olive-shell, however, is marked by several prominent 

 oblique folds, and the outer lip is not rolled in as it is in 

 the Cowries. The animals of the two families, moreover, 

 differ in several respects, but most markedly in the 

 structure of the odontophore. An operculum is commonly 

 absent. 



15th Family, Voiutidae [Cases 165C — 166B]. 



This family includes the large " Boat-shells " and 

 " Melon-shells " of the Indo- Pacific shores. It also includes 

 the small cowrie-like Marginellas, which, however, can 

 always be distinguished from cowries by the oblique folds 

 on the inner lip that characterize all the Volute shells. 



NATANTIA. 



[(Ense 1660^]. 

 In the Section of Swimming Azygobranch Gastropods, 

 which corresponds to the Order Heteropoda of authors, 



