236 PALAEONTOLOGY. 



the supposition that there is any process of development 

 from lower to higher forms. 



"We find some families prevailing at one period more than 

 at another ; for example, the trigonece in the oolitic. The 

 pernce and gryphece in the neocomian rocks. 



The most remarkable changes, however, have taken place 

 in species at different periods. Thus Dr. Grant * has shown, 

 in an analysis of Deshayes' labours on tertiary shells, that 

 "nearly a thousand fossil species of concJiifera have been 

 obtained from the tertiary strata, and more than a seventh 

 part of these are found to be identical with living species of 

 the same or of distant latitudes. Seventy-two species of 

 ostrea have been observed in tertiary strata of Europe, and 

 of these, seven are identical with species now living in the 

 ocean ; of sixty tertiary fossil species of pecten, thirteen are 

 identical with the living ; of fifty-four tertiary species of 

 area, thirteen are also recent ; of fifty tertiary venericardite, 

 six are still living ; of fifty-nine cytherce, ten are recent ; of 

 fifty-nine lucina, nine are recent ; of fifty-four telling, twelve 

 are recent ; of thirty-five corlulce, one is recent ; of forty- 

 three veneres, nine are recent ; of thirty -nine cardia, seven 

 are recent ; of twenty-seven pectunculi, four are recent ; of 

 twenty-three nuculte, four are recent; of twenty chamce, 

 four are recent; and of twenty-one tertiary species of modiola, 

 three are found to be identical with the existing species. 



"But in the same genera of bivalved mollusca the number 

 of species found imbedded in the tertiary strata often 

 exceeds that of the species now known in a living state : 

 thus, twenty-three species of nucula are met with in the 

 tertiary strata, and only seven species are now known in a 

 living state ; there are fifty known tertiary species of veneri- 

 cardium, and only twenty-five recent species; there are 

 nineteen tertiary species of astarte and only three recent ; 

 fifty-nine tertiary lucinee, and twenty living ; thirty-five 

 tertiary corbulce, and ten recent ; twenty-three tertiary 

 erycintB, and three recent ; twenty-four tertiary crassatellce, 

 and nine recent. In many of the other genera of this class, 

 the number of recent species much exceeds that of the 

 species hitherto found in the tertiary strata; thus one 



* Thomson's British Annual, 1832, p. 245. 



