248 MOLLUSCA. 



of the Red Crag (Newer Pliocene) is the reversed shell, 

 Fusus contrarius, which is now known to exist in the living 

 state as well. 



Fig. 209. fusus Necomiensis. Fig. 210. Buccinum undatum (var.) 



Lower Greensand. Post-Pliocene and Recent 



FAM. 3. BucciNiD^E. Shell notched anteriorly, or with the 

 canal reflected, producing a kind of varix on the front of the 

 shell. With the exception of the extinct genus Piirpurina of 

 the Lower Oolites, and some species of Buccinum in the Cre- 

 taceous Rocks, the family of the Bucdnidce. is exclusively con- 

 fined to the Tertiary and Recent periods. The two great 

 families, therefore, of the Muricidoe and Bucdnidce are essen- 

 tially characteristic of the later periods of the earth's history. 

 The most important fossil genera of the Buccinida are Buc- 

 cinum, Terebra, JVassa, Purpura, Cassis, and Oliva. 



The Whelks form the genus Buccinum (fig. 210), dis- 

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

 short reflected canal. Some few species of Buccinum are 

 found in the Upper Cretaceous Rocks ; but the genus is 

 essentially Tertiary and Recent. 



Terebra comprises the Auger-shells, distinguished from the 

 Whelks by their long, pointed shells, consisting of many whorls, 

 and having a small mouth. They commence in the Eocene 

 Tertiary. The Dog-whelks (Nassa) 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. The shells of the genus Purpura 



