54 



CASSIS.— TEREBRA.—CERITHIUM. 



called, which it very much resembles. The shell is ovate, thick, 

 most frequently tuberculated, and characterized by its flattened 

 columella, which is trenchant towards the end opposite to the 

 spire, and forming, at that point with the external margin of the 

 aperture, an unprojecting canal. 



Fig. 61. CASSIS. Fig. 62. 



7. The Helmet — Cassis {Jigs. 34, 61, 62) — also very 

 much resembles the ordinary Buccinum ; but their shell, which 

 is ovate, with a short, slightly projecting spire, is furnished with 

 a transversely wrinkled plate, covering the 

 columella, like the Nassa. The aperture, 

 sometimes oblong, sometimes straight, is 

 also wrinkled externally, and its notch termi- 

 nates in a little short canal which is curved 

 backwards. 



6. The Terebra differs still less from the 

 Buccinum properly so called : it is distin- 

 guished from it only by the elongation of its 

 spire. 



9. The Cerithium (fg. 63), the shell of 

 which is turreted, like that of the Terebra, but 

 furnished with a short canal curved to the left 

 or backwards, also differs from other Buccina 

 by having a veil above the head : this animal 

 has but a single branchia. Some of the mol- 

 lusks of this genus inhabit the sea, and others 

 fresh water. A great many living species are 

 known ; but they were formerly more abun- 



Fig. 63. 



CERITHIUM ALUCO. 



7. What are the characters of the genus Cassis? (Cassis, Latin, a 

 helmet.) 



8. How is Terebra distinguished from Buc'cinum ? (Buccinum, Latin, 

 a trumpet, a shell-fish.) 



9. What are the characters of Cerithium ? 



