MARINE MOLLUSCS 



247 



beaches, where it devours small bivalves and other animals ; and 

 it is frequently washed up alive by the waves. Its shell is also a 

 favourite one with hermit crabs. Its eggs, all connected together 

 in a spiral band, may often be seen stranded on sandy coasts. 

 Several species of Natica are found on our shores. An allied 

 mollusc Velutina Icevigata, so called on account of the velvety 

 epidermis that clothes the shell, completely surrounds the shell by 

 its mantle folds when creeping. 



The Siphonostomata form a much smaller section than the 

 last, and its members are distinguished mainly by the presence 

 of a true siphon, formed by the prolongation of the mantle margin, 

 and serving to convey water into the gill chamber. In all these 

 the shell is spiral, usu- 

 ally without an umbilical 

 opening, and the margin 

 of the mouth is prolonged 

 into a canal or distinctly 

 notched. The operculum 

 is horny, and lamellar or 

 imbricated. The animal 

 has a retractile proboscis, 

 and the eyes or eye- 

 pedicels are joined to 

 the tentacles. All the 

 species of this division 

 are marine. 



We will first take the family Cyprceidce, which contains the 

 familiar Cowries, these forming the lowest group of the division. 

 An examination of the shells may at first seem rather puzzling, 

 for the spire is concealed, and the whole is convoluted in such 

 a manner as to make the mouth long and narrow, with a channel 

 at either end. The outer lip is also thickened and bent inward, 

 and there is no operculum. 



The animal itself is particularly interesting, for, as it creeps 

 along on its broad foot, abruptly shortened in the front, the 

 mantle lobes bend over the top, meeting along the middle line, 

 where they are usually fringed with little tentacle-like processes ; 

 and, as a result, the whole 'shell is beautifully enamelled on the 

 outer surface. In all the Cowries the central teeth are single, and 

 the laterals are arranged either in twos or threes. 



Perhaps the commonest representative of this family is the 



FIG. 178. Cypma (Trivia) europcea 



