250 MOLLUSCA. 



terised by the short spire, large, deeply-notched aperture, and 

 columella with several plaits. Species of Valuta occur in the 

 Cretaceous period, but the genus is mainly Tertiary and Recent. 



In the genus Mitra the shell is spindle- 

 shaped, with a long spire, and small 

 mouth. The Mitrce commence in the 

 Cretaceous period, but the fossil species 

 are mainly distributed through the Ter- 

 tiary formations. 



FAM. 6. CYPR^ID^E. Shell convo- 

 lute, 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 

 Fig. 2i2.^cyp>-cea eiegaus. meet over the back of the shell. The 

 only important genus of this family is 

 that of Cyprcea (fig. 212), comprising the numerous and well- 

 known living shells which are commonly called Cowries. The 

 Cyprace are mainly, but not exclusively, inhabitants of warm 

 seas, and they attain their highest development 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. 212) 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 

 Cyprcza Eiiropcea is the type, are not known as occurring in the 

 fossil condition. 



Division b.Holostomata. Margin of the shell-aperture "entire" 

 rarely notched or produced into a canal. 



FAM. 7. NATICID^E. Shell globular, of few whorls, with a 

 small spire ; outer lip acute ; inner lip (pillar) often callous. 

 Foot very large ; mantle-lobes hiding more or less of the shell. 

 This family is stated to commence in the Upper Silurian 

 Rocks ; but there is more or less uncertainty as to the true 

 affinities of the Palaeozoic fossils which are referred here. 

 The most important fossil genus is Natica itself. 



The shell in Natica (fig. 213) is thick, smooth, and polished, 

 often with coloured markings. The inner lip is callous, and 

 the shell is umbilicated. Fossil Naticce have been described 

 from the Upper Silurian, Devonian, Carboniferous, and Per- 

 mian Rocks; and they are very abundant in all the Secondary 



