14 



GASTEEOPODA. 



Eecent. There are several sub-genera of Voluta, the most 

 important being the Eocene VolutilitJies, with its many- 

 whorled spire. In the genus Mitra 

 the shell is spindle-shaped, with a long 

 spire and small mouth. The Mitne 

 commence in the Cretaceous period, but 

 the fossil species are mainly distributed 

 through the Tertiary formations. Col- 

 urribellina and Lyria are Cretaceous ; 

 and the living genera Volvaria and 

 Margindla begin in the Eocene. 



Fam. 6. Cypr^id^. — Shell convol- 

 ute, enamelled ; spire concealed ; aper- 

 ture narrow, channelled at each end. 

 Outer lip thin in the young shell, but 

 thickened and inflected in the adult. 

 Foot broad; mantle forming lobes which 

 meet over the back of the shell. The 

 only important genus of this family is 

 that of Cyprcca (fig. 394), comprising 

 the numerous and well-known livino' 

 shells which are commonly called Cow- 

 ries. The Cyprccm are mainly, but not 

 exclusively, inhabitants of warm seas, 

 and they attain their highest develop- 

 ment between the tropics. The fossil 

 species date from the Cretaceous period, and abound in the 

 Tertiaries. 



The shell of the Cowries in the young state is furnished 

 with a prominent spire, and has a thin outer lip. In the 

 adult state (fig. 394) the spire is completely concealed within 

 the shell, the entire surface is generally covered with shining 

 enamel, the inner lip is crenulated, and the outer lip is thick- 

 ened, inflected, and crenulated. The small Cowries of which 

 Cyprwa Eurojpma is the type, are not known as occurring in 

 the fossil condition. Ovulmn, dating from the Eocene, re- 

 sembles Cyprcca, but the inner lip is smooth. 



Division h. Holostomata. — Margin of the shell - aperture 

 " entire" rarely notched or ■prodv.eed into a caned. 



Fig. 393. — Voluta elongata. 

 Chalk. 



