Molluscs of the isles Sechelles and Amirantes. 97 



fossil conchology by the distinction and denomination of 

 species, many geologists, often but little acquainted with na- 

 tural history, have claimed acquaintance with this depart- 

 ment of science, and afterwards, rather elicited by the ne- 

 cessity of combining this branch with geology, than refin- 

 ed by real knowledge in zoology, they have established, and 

 denominated as species a great number of fossil shells, 

 without sufficiently understanding the limits of variation of 

 which these molluscous creatures are susceptible, and in- 

 deed, before malacology was itself in a fit state to supply the 

 wants of science. 



An individual amongst us during the few years he 

 officiated for M. de Lamarck in the Museum of Natural 

 History, having perceived how much it was important to 

 scrutinize their limits of variation before proclaiming their 

 laws, had commenced to establish groups of shells of the 

 same species, being guided not only by age, but even by 

 sex in diocious species, as well as locality ; but M. Dufo 

 directed by these efforts has gone much further. We 

 remark indeed in the collections of shells made by this 

 zealous observer, the succession of a great number of 

 species, the shades of which amount to more than fifty, and 

 their differential shades have not only relation to the size 

 or stature, but also on all the differential peculiarities 

 which the shells can offer. So that in this respect, 

 more especially in the genera Purpura, Ricinula, Tur- 

 benella, Murex cypraea, Strombus, Pterocera, the collec- 

 tion of M. Dufo is of great interest, because it permits 

 us to appreciate the limits by variation which a species 

 of shell is susceptible even in climacterical circumstances 

 and others absolutely the same. What, if he had been able 

 to reunite the varieties which the same living species may 

 offer at a more or less considerable distance ? 



Besides these two important points regarding malacology, 

 M. Dufo has also directed his attention to many others which 



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