M. B. de Basterot's Observations on Fossil Shells. 103 



come sufficiently advanced to furnish us with numerous and 

 well-authenticated facts." Now this knowledge of species is 

 almost entirely wanting as respects the Mollusca. It is but a 

 short time since, that the search for shells has become, from a 

 simple amusement, the study of scientific men : it was only 

 after the period when it was perceived that geology and an- 

 cient zoology were destined to be enlightened by their fossil 

 remains, that this research passed from the hands of amateurs 

 into those of naturalists. From this period, the number of 

 fossil species observed by naturalists and inscribed in their 

 catalogues, has increased with astonishing rapidity. 



The thirteenth edition of the Sy sterna Naturae cites only 

 fifty-three species as found in a fossil state, ten of which were 

 analogous to those at present existing. At the moment I 

 write (1824) I possess a MS, list of the fossil species described 

 by authors, the number of which amounts to more than 2500, 

 — the distribution of which will be seen in the following table. 



Number of genera 



the species of which 



are found fossil. 



2 ("Chambered 29 



H < Univalves 81 



^ ( Multivalves and bivalves 111 



221 2529 264. 



I am unable to present equally exact details on the aug- 

 mentation of living species known to naturalists, but it no doubt 

 forms a much less considerable proportion. The same edition 

 of the Systema Naturcc does not quite contain 2400 species, 

 — a number smaller than that at present presented by the fos- 

 sil species, collected almost entirely in France, England, and 

 Italy. This should lead us to hope, that when the attention 

 of travellers is awakened to this subject, they will bring us 

 from distant countries an abundance of species as yet unknown 

 in our collections. 



What lias been above stated will be sufficient to prove, that 

 our knowledge of the species of the molluscous class is not yet 

 sufficiently advanced to allow us to hazard generalities on their 

 geographical distribution. I may, I hope, nevertheless be 

 pardoned in adding some observations which may add new 

 interest to this kind of research. 



In fact, the geographical distribution of living families, 

 genera, and species, compared with the actual distribution of 

 lossil species, may throw light on many of the most imjiortant 



geological 



