FOSSIL INVERTEBRATED ANIMALS. 453 



pierced by shells or perforating animals like the ancient lime- 

 stones found in the Mediterranean. 



In some localities there are beds of the coarse limestone 

 which are composed only of miliolites, and other very small 

 marine bodies^ either entire or in debris, without any other 

 mixture, and always without any adherence. A stratum of 

 this kind is found at Beyne, near Grignon. The strata ante- 

 rior to the chalk exhibit nothing analogous, either in the 

 smallness of the marine bodies or in the want of cohesion 

 between them. Where these last were found, the species 

 were not equally numerous, nor do they appear in general to 

 have been so small. 



It may be remarked, in general, that in the strata anterior 

 to the chalk, bivalve shells are to be found with their two 

 valves very often united, or the internal mould of these two 

 valves, which proves that they were so at the moment of petri- 

 faction. This is not the case in the other strata, and especially 

 in that of the coarse limestone, where it is very rare to find 

 bivalve shells entire, and there is, perhaps, no exception to 

 this but in the stratum of the Placentine territory. 



It has been remarked that organic bodies, found in the fossil 

 state, differed from those now existing in proportion to the 

 antiquity of the strata in which they were discovered. This 

 remark is fully confirmed by a summary view of the living and 

 fossil genera, and the peculiar circumstances in which the 

 latter are placed. We find, that out of five hundred and two 

 genera of polyparia, stellerides, echinodae, annelides, serpulse, 

 cirrhipedes, and shells, eighty-nine genera are not found in 

 the fossil state ; two hundred present themselves both in the 

 living and fossil states, and one hundred and fifteen in the 

 fossil only. On uniting these two last numbers, and observing 

 in what particular strata they are met, we find one hundred 

 and thirty-four genera in the most ancient strata, seventy-five 

 in the chalk, and two hundred and three in the strata posterior 

 to that substance. If we examine in what strata are to be met 



