Molluscs. 



lateral lobes. As in the Pelecypods, there is no distinct head ; 

 eyes and gills are also absent. The sexes are separate. The 

 Tusk-shells may be found living buried in mud or soft sand 

 on the limit of low-water mark, and empty shells are among 

 the common objects of the beach in some localities. When 

 buried, the posterior or thinner extremity of the shell projects 

 to give access to the respiratory current. 



FIG. 36. TOP-SHELL, TROCHUS 



ZIZYPHINUS (after WOODWARD). 



