IN THE MOLLUSC A. 133 



strictly natural. But when we examine the creatures 

 of which these shells are the covering, we find them 

 so differently organized that it is impossible to regard 

 them as of the same genus. It would therefore be just 

 as natural, classing quadrupeds by their skins, to place 

 the leopard and the camelopard in the same genus be- 

 cause they have similar coats, as it would be to com- 

 bine, under one group, the various species of the Lin- 

 nsean genus Patella. Conchology, within a few years, 

 has made more advances in a philosophical direction 

 than most of the other natm*al sciences. Up to a re- 

 cent period, it was the lowest of all scientific pursuits, 

 and appeared the most useless. Now, however, that 

 the subject begins to be studied on better pi-inciples, a 

 new light has burst upon it, and a thousand interesting 

 facts in the lives of the shell-coated animals are re- 

 vealed. 



Nor is the interest which attaches to Conchology 

 merely derived from our increased knowledge of the 

 habits and instincts of an extensive class of animals. 

 Its bearings on Geology place it among the most import- 

 ant of the minor divisions of Zoology. Shelly-coated 

 Mollusca have existed in the waters of the sea and of 

 rivers from a very early period of the world's history, and 

 have left in most stratified rocks and gravels abundance 

 of their shells, preserved in a more perfect manner than 

 the remains of most other animals. Now, as the species 

 in the early rocks differ from those found in later forma- 

 tions, quite as much as the latter from the Mollusca of 

 our modern seas, the gradual change in the character 

 of the imbedded shells marks a certain interval of time 



