and on the Fossil Remains contained in them. 149 



genus. ^ bivalve, vearhj circular, the margin turning up- 

 wards so as to give it a patella or disk form, with numerous 

 long processes passing from the viargin and external sur- 

 face, and fixing it to other bodies. A small pccten ivith 

 sharp ungulated riJ'S, not exceeding a quarter of an inch in 

 length. A bivalve, not an eighth of an inch in length, 

 finely striated longitodinallv, hearing a hright polish, and 

 seeminijly possessincj its original light brown colour. Flates 

 of the lorfoise evhinite, and several remains apparently of 

 other species of this genus. 



When to these are added the remains of various echini, 

 sucha.?.conulites,cassid/tes, and spatangites, and ihe different 

 spines oi echini which are found in this stratum; and when 

 it is also considered that the present account is drawn up 

 almost entirely from the produciions of chalk clifTs, of not 

 more than two miles in lengiii, it will not he difficult to 

 conceive, that the number of these fossils is not less in the 

 English than in the French chalk. 



The Slate in which these fossil;; arc found, plainly fvinces 

 that the matrix in whicli they are imbedded was formed by 

 a gradual deposition, which entombed these animals whilst 

 living in their native beds. The fine and delicate spinous 

 projections of the shells are unbroken, and the spines are 

 still found adhering to the crustaceous coverines of the 

 echini; neither of which circumstances could have occurred 

 had these bodies been suddenly and rudely overwhelmed by 

 these investing depositions, or had they been brought hither 

 from distant spots. 



It may be said that the specimens possessing the characters 

 here alluded to are rare. With respect to the spinous shells, 

 however, they certainly occur often, although it is almost 

 impossible to extricate them unbroken from tlieir surround- 

 ing chalk ; and the rarity of the spcciniens of echinites with 

 their attached spines, depends in a great measure on the 

 mode in which these specimens are obtained. The speci- 

 mens seen in cabinets are seldom found by the naturalist 

 himself, but are preserved by the work people, who break 

 the chalk when any unconmion appearances catch their 

 eye. Hut it fi'equently happens that these marks are not 

 seen until the piece is broken by their tool, and with it, 

 perhaps, the entire animal. 



The perfect slate of the surfaces of the chalk fossils proves 

 also that thii; deposition proceeded from the surroundingr 

 fluid, and that it was not derived from the immediate action 

 of any chenjicalagent on the shells and other calcareous 

 coverings of ihe animals livins: at th* bottom of the sea. 



^^i in 



