CRISTACEA. 12/ 



they are from the CrepidulaB. Fig. 239. Mediterranean, North 

 and South America, East and West Indies, New South Wales, &c. 



CREPIDULINA. Bl. Cristellaria, Lam. Microscopic. 



CRESEIS. Ranz. Order, Pteropoda, Lam. — Descr. Thin, fra- 

 gile, transparent, pyramidal, pointed ; with a dorsal ridge pro- 

 duced into a point at the edge of the aperture. — Obs. The species 

 found in the Mediterranean is named C. Spinifera (fig. 222), 

 from its resemblance to a thorn. 



CKEUSIA. Leach. (Creux, se. Fr. a cavity.) Fam. Balanidea, 

 Bl. Order, Sessile Cirripedes, Lam. — Descr. A depressed cone, 

 consisting of four valves, supported upon, and jointed to, a cup- 

 shaped cavity formed in the Madrepores, in which it resides. 

 Aperture quadrilateral, closed by an operculum of four valves. — 

 Obs. This genus is distinguished from Pyrgoma, which is sup- 

 ported on the edge of a similar cup-shaped cavity, by the paries 

 being composed of four valves, whereas in Pyrgoma, it consists 

 of a single piece. Fig. 28, C. Gregaria. East Indies. 



CRICOSTOMATA. Bl. The second family of Asiphonibranchiata, 

 Bl. It is thus described : " shell equally (with the animal) va- 

 riable in general form, but of which the aperture, always nearly 

 round, is completely closed by the shelly or horny operculum ; 

 whorls few, and apex sublateral." This family agrees in some 

 measure with the family Turbinacea of Lamarck, and with the 

 genus Turbo in the system of Linnseus. It contains the genera 

 Pleurotomaria, Delphinula, Turritella, Proto, Scalaria, Vermetus, 

 Siliquaria, Magilus, Valvata, Cyclostoma, and Paludina. 



CRIOCERATITES. A genus composed of species of Ammonites, 

 with disconnected whorls. C. Duvallii, fig. 482. 



CRIOPUS. Poli. Crania, Auct. 



CRISTACEA. Lam. The third family of Polythalamous Cephalo- 

 poda, Lam. This family is described as including shells of the 

 following characters : — " Multilocular, flattened, nearly reniform ; 

 the chambers gradually increasing in length, as they approach 

 the outer arched margin, and appearing to revolve round an ec- 

 centric, more or less marginal axis. The Cristacea contain the 

 genera Renulina, Cristellaria, and Orbiculina." 



