102 CERITHIUM. 



are destitute of shells ; the second composed of those microscopic 

 cellular bodies, which are regarded as shells by some authors ; 

 and the third containing the true chambered shells. 

 CEPHALOPODA. Lam. (Cephalopodes.) (Ke^aX^, kephale, head ; 

 kovq, ttqSog, podos, foot.) The fourth order of the class Mol- 

 lusca, Lam. containing molluscs, which are characterized by 

 having a series of arms snrrounding the head, which is placed 

 above a sack-shaped body. This order is divided into Poly- 

 thalamia, or many-chambered shells ; Monothalamia, or single- 

 chambered cephalopods ; and Sepiaria, or cuttlefish. Fig. 4G3 

 to 488. 

 CEPOLIS. Montf. Belonging to the genus Helix, Auct. 

 CERATODES. Guild. (Kepar^rjg, like a horn.) A genus com- 

 posed of the flat, orbicular species of Ampullaria, Auct. 

 which present so near a resemblance to the Planorbes, as to have 

 been considered as belonging to them. Planorbis has, however, 

 a horny texture, and no operculum, and it is always reversed, 

 which may be observed by placing the spire upwards . Fig. 320, 

 represents Ampullaria (Ceratodes) Cornu-arietis. 

 CERIPHASIA. Sw. A sub-genus of Melanianse, thus described, 

 " Cerithiform ; outer lip thin, dilated at the base ; aperture 

 small, slightly emarginate, without any internal groove ; inner 

 lip thin. C. sulcata, Sw. fig. 38. p. 204." (Sw. Lard. Cyclop. 

 Malac. p. 342.) 

 CERITHIUM. Brug. Fam. Canalifera, Lam. Entomostomata, 

 Bl. — Desc. Elongated, ribbed, tuberculated, or rarely smooth, 

 with a lengthened, turrited, pointed, pyramidal spire, consisting 

 of numerous whorls ; aperture sub-quadrate, terminated ante- 

 riorly by a tortuous canal ; outer lip thickened, sometimes re- 

 flected, expanded ; inner lip thickened posteriorly ; operculum 

 horny, spiral, with numerous whorls. — Obs. The fresh-water 

 shells described as Cerithia by Lamarck, are separated under the 

 name Potamis, and may be known by the thick, horny epider- 

 mis. Triphora, Desh. has the canal closed, except at the ex- 

 tremities. Cerithium Telescopium, does not appear to present 



