104 CEEIPHASIA. 



impression of a bivalve shell when it is near the centre of the 

 inner surface. It is also applied to the siphon perforating the 

 septum of a chambered shell when it is placed near the centre of 

 the plate. Sub-central is also used as a comparative term, to 

 indicate the position of the siphon, or of the muscular impres- 

 sion, is neai' the centre. Thus in Placuna (fig. 184), the muscular 

 impression is central : in Exogyra (fig. 183), it is sub-central. 



CEPA. Humph. 1797. Anomia, Linn. Muller. 1776. 



CEPHALOPHOEA. Bl. The first class of Malacozose, Bl. Di- 

 vided into: Order 1. Cryptodibranchiata ; 2. Cellulacea; 3. 

 Polythalamacea. The first consisting of Cuttle-fish, &c. which 

 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^aXri, hephale, 

 head ; Trowe, ttoSoc, podos, foot.) The fourth order of the class 

 MoUusca, Lam. containing molluscs, which are characterized by 

 having a series of arms surrounding 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 Cephalopoda : and Sepiaria, or cuttle fish. Pig. 463 



" to 488. 



CERATISOLEN. Eorbes. Phaeus, Leach. Ms. Gray. Syn. 

 Brit. mus. A genus formed for the reception of Solen legumen, 

 which differs from the true Solens, or razor shells, in having 

 the umbones nearly central, &c. 



CEB,ATODES. Guild. 1828. Marisa, Gray. 1824. (Keparwgijc, 

 like a horn.) A genus composed of the flat, orbicular species of 

 Ampullabia, 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. PL xv. fig. 320, represents Ampullaria 

 (Ceratodes) Cornu-arietis. 



CEEIPHASIA. Swainson, 1840. A sub-genus of Melanianae, 

 thus described, " Cerithiform ; outer lip thin, dilated at the base ; 

 aperture small, slightly emarginate, without any internal groove ; 



