GASTEROPODA. 



11 



earth's liistory. The most important fossil genera of the 

 Buccinidce are Buccinum, Terebra, Nassa, Purpura, Cassis, 

 and Oliva. 



The Whelks form the genus Buccinum (fig. 390), distin- 

 guished by the ventricose body-whorl, large aperture, and 

 short reflected canal. Some few species of Buccinum are 

 found in the Cretaceous rocks ; but the genus is essentially 

 Tertiary and Eecent. 



Terebra comprises the Auger-shells, distinguished from the 

 "^Yhelks by their long, pointed shells, consisting of many 



Fig. 391. — A, FiLsispira terebriformis — Lower Silurian (after Hall); B, Nassa ptisillina — 

 Pliocene (after Searles Wood) ; c, Ringiaula venfricosa — Pliocene (after Searles Wood) ; d, Ful- 

 gur canaliaulatus — Miocene ; e, Pyrula reticulata — Pliocene ; r, Fusiis contrarius — Pliocene ; 

 G, Pv.rpii/ra tetragona — Pliocene (after Searles Wood) ; h, Subulites terebriformis — Upper Silu- 

 rian (after Hall). 



whorls, and having a small mouth. They commence in the 

 Eocene Tertiary. The Dog-whelks {JVassa) also commence 

 in the Eocene, and are distinguished from the Whelks chiefly 

 by having the columellar lip expanded and callous, with a 

 tooth near the anterior canal (fig. 391, b). The shells of 

 the genus Purpura (fig. 391, g) have a short spire and wide 



