158 



CHAPTEE XXYI. 



CLUB-SHELLS. — CEEITHIUM, — BRITISH SPECIES. — PELICAN's FOOT APOR- 

 RHAIS. EYES AND EARS OF STROMBID^. 



CEBITHIADJE. 



I. Cerithium. — Our Chth-sheUs, as the members of this 

 group are called^ from their shape, certainly do not present 

 the idea of very formidable weapons, the largest of British 

 species hardly exceeding half an inch in length. We are 

 now entering the series, the shells of which terminate in a 

 sinus or canal in the aperture of the shell, corresponding 

 either with a fold in the mantle or a distinct siphonal tube. 

 The eyes of CeritJdum are placed on prominent bulgings 

 near the bases of two rather stout tentacles, which take 

 their rise at the back of the snout-shaped head ; the foot 

 bears a horny, spiral operculum, and the mantle has a fold 

 or sinus at its front edge, which is not however produced 



