66 M. Dufo on (he Mollusca of the 



of the opening, had caused to be separated from the Oerithiums, 

 which are marine. In truth, C. palustre, as the name indicates, 

 inhabits the fresh waters of marshes. 



Science will likewise be indebted to M. Dufo for a positive 

 knowledge of the fact, that the operculum is wanting in the 

 genus Terehelhim (T'arier^), which formerly rested on supposition 

 merely. 



The second point on which M. Dufo's observations have 

 most essentially borne, is that of the successive forms through 

 which shells pass, from the earliest age of the animal which 

 bears them, till its decay. This is a point of extreme import- 

 ance, and evidently connected with the fact of the diminution 

 of the lobes of the mantle with age, as M. Dufo has again con- 

 firmed. 



In truth, from the time that geology, while passing into the 

 state of a science, acquired, in the organized bodies whose 

 fossil remains exist in the superficial strata of the earth, 

 one of the most powerful means for solving the problems of 

 the identity or antiquity, or even the origin of these strata, 

 the study of shells, which, from their chemical nature, may 

 form extensive rocks, has acquired a very great importance. 

 But, unfortunately, since M. Lamarck, so justly celebrated, 

 has regulated fossil conchology by the distinction and naming 

 of the species, many geologists, who are often but little ac- 

 quainted with natural history, have seized upon this part of 

 the science ; and then, sometimes constrained rather by the 

 wants of geology than enlightened by a real knowledge of 

 zoology, they have established and named as species a great 

 number of fossil shells, without taking into account the limits 

 of variation which those parts of molluscous animals undergo, 

 and, in fact, before malacology was at all in a condition to 

 meet the wants of science. One of ourselves, during the few 

 years he occupied the place of M. Lamarck in the Museum of 

 Natural History, having felt how important it was to examine 

 the limits of variation, before adducing laws, had begun to 

 form series of shells of the same species, having a regard not 

 only to the age, but likewise to the sexes of the dioecious kinds, 

 as well as to their localities. Guided by these attempts, M. 

 Dufo has gone much farther. In the collection of shells brought 



