C R A 



L 



generally on the chalk. By some 

 the crag has been divided into two 

 groups, the lower, or coralline, 

 which is, in some places, fifty feet 

 or more in thickness, and the 

 upper, or red crag, thus named 

 from its ferruginous colour. The 

 fossils of the crag are very nume- 

 rous. From an examination of a 

 collection of shells of the crag made 

 by M. Deshayes, it appears that 

 out of 111 species, 66 were extinct 

 or unknown, and 45 recent, the 

 last, with one exception, being in- 

 habitants of the German Ocean. 

 From this result Sir C. Lyell 

 concludes that the crag belongs to 

 the olden Pliocene period. 



The sands of this formation vary 

 in colour from white, through 

 different shades of yellow, up to 

 orange-red : the colour proceeding 

 partly from a ferruginous stain, and 

 partly from the intermixture of 

 yellow oxide of iron. 



CEA'NIA. (from cranium, Lat. a 

 skull, in consequence of a supposed 

 resemblance of the interior of the 

 shells to a skull, arising from some 

 deep muscular impressions.) A 

 regular inequivalved bivalve ; the 

 upper valve very convex, patelli- 

 form, with the umbo near the 

 centre, the lower valve flat, and 

 nearly round, and pierced internal- 

 ly with three unequal and oblique 

 holes. The arms of the animal are 

 ciliated. Cuvier places crania in 

 the class Brachiopoda, division 

 Mollusca. By Lamarck this genus 

 is placed in the family Rudistes, 

 order Monomyaria ; and by De 

 Blainville in the order Palliobran- 

 ehiata. Craniae are found attached 

 to stones and shells, and are 

 brought up, probably from great 

 depths, by cod-lines, off the coast of 

 Shetland, and with corals in the 

 Mediterranean. Several species of 

 fossil cranise are found in the chalk 

 formation. 



CBA'SIDH. (Lat.) The skull. 



2 ] ORE 



CEASSATE'LLA. (from crassm, thick, 

 Lat.) A genus of equivalved in- 

 equilateral close bivlaves. The 

 hinge teeth two, with an adjoining 

 fossa; the lateral teeth obsolete. 

 The cartilage inserted in a pit 

 formed in the hinge. 



As the crassatella advances in 

 age, the valves become very greatly 

 thickened, from which circumstance 

 it obtains its name. Cuvier places 

 this genus in the family Mytilacia, 

 order Acephela ; Lamarck, in the 

 family Mactracea; and De Blain- 

 ville, in the family Conchacea. 



Recent crassatellas inhabit sandy 

 mud at depths varying from eight 

 to twelve fathoms. Some species 

 of fossil crassatellae have been 

 found in the tertiary formations. 



CEA'SSINA. The name assigned by 

 Lamarck to a genus of shells. See 

 Astarte. 



CRE'NATE. } (crenatus, Lat.) Notched 



CEE'NATED. j at the margin ; scol- 

 loped ; indented. 



1. It is applied to leaves when 

 the notches or teeth on the borders 

 are rounded, and the notches not 

 directed to either end of the leaf. 



2. In entomology, a margin with 

 indentations, not sufficient to be 

 called teeth, the exterior whereof 

 is rounded. 



CBE'NATTTEE. The notch or indenta- 

 tion of a leaf. 



CEEN'ATULA. (from erenatm, Lat.) 

 This name has been given to a 

 genus of bivalves from the hinge 

 showing a row of roundish or oval 

 pits, making it appear as if crenu- 

 lated. An irregularly formed flat 

 bivalve ; closed, not giving passage 

 to any byssus ; the hinge linear, 

 excavated, and crenulated ; um- 

 bones terminal. It is found in 

 sponges, and moored to coral-lines, 

 &c. Parkinson, in describing the 

 crenatula, says, "there are very- 

 few among the fossil shells of this 

 or of any other country, which, at 

 first sight, are more dissimilar 



