242 MANTJAL OF THE MOLLrSCA. 



beloTv; outer lip tMn, inner lip wanting, columella callous, 

 slightly tortuous. 



Type, M. arculatus, Schlotheim species. Devonian. Eifel. 



Distribution, 1 species (M. Japonicus), Korea Straits. 



Fossil, 12 species. Devonian — Carboniferous. Britain, 

 Belgium. 



Family III. — CERixHiADiE. Cerites. 



Shell spiral, elongated, many-whorled, frequently varicose ; 

 aperture channeled in front, with a less distinct posterior canal ; 

 lip generally expanded in the adult; operculum horny and 

 spiral. 



Animal with a short muzzle, not retractile ; tentacles distant, 

 slender ; eyes on short pedicels, connate with the tentacles ; 

 mantle -margin with a rudimentary siphonal fold ; tongue 

 armed with a single series of median teeth, and three laterals 

 or uncini. Mr. Wilton has examined the dentition of four 

 Cerithiadce ; the teeth are broad, as in Melaniadoe, with incurved 

 and dentated summits. In Ceritkidium the median teeth are 

 slender with minute hooks. Habitat. Marine, estuary, or fresh 

 water. 



Cerithiiim (Adans.), Bruguiere. 



Etymology, ceration, a small horn. 



Type, C. nodulosum. PI. YIII., Fig. 16. 



Shell turreted, many-whorled, with indistinct varices ; aper- 

 ture small, with a tortuous canal in front ; outer lip expanded ; 

 inner lip thickened; operculum horny, paucispiral. PI. YIII., 

 Fig. 16.* 



Distribution, 136 species. World-wide, the typical species 

 tropical. Norway, Britain, Mediterranean, West Indies, India, 

 Australia, China, Pacific, Gallapagos. 



Fossil, 460 species. Trias — . Britain, France, United 

 States, &c. 



Sub-genera. Rhinodavis, Sw. C. vertagus. Canal long, 

 bent abruptly ; operculum, sub-spiral. 



Bittium, Leach. C. reticulatum, PI. VIII., Fig. lY. Small 

 northern species, ranging from low water to 80 fathoms. 



Triforis, Deshayes. C. perversum, PI. YIII., Fig. 18. 30 

 species. Norway — Australia. 



Fossil, Eocene — . Britain, France. 



Shell sinistral ; anterior and posterior canals tubular. Tho 

 third canal is only accidentally present, forming part of a 

 Tarix. 



Cerithiopsis, Forbes. C. tuberculare, Britain. 



