Sechellea and Amifantes Islands. (17 



by this zealous observer, we observe series of a considerable num- 

 ber of species, the variations of each of which amount to upwards 

 of fifty ; and the variations affect not only the size, but all the 

 distinctive peculiarities which shells can present. In this re- 

 spect, M. Dufo's collection is of great interest, particularly in 

 the genera Purpura, Ricinula, Turbinella, Murex, Cyprsea, 

 Strombus, and Pterocera, since it enables us to appreciate 

 the limits of variation of which one species of shell is suscep- 

 tible, even in climateric and other circumstances absolutely 

 alike. To what would this lead, if to these were added the 

 varieties which the same species exhibits when living in moi*e 

 or less distant localities I 



Besides these two important points in malacology, M. Dufo 

 has directed his attention to many others not less interesting, 

 and has filled up some blanks in the natural history of the 

 mollusca. 



Thus the (tepth and nature of the parts of the sea which 

 different mollusca prefer, have been carefully noted by M. 

 Dufo. He has remarked, for example, that the bivalves which 

 live in the sand bury themselves deeper as they advance in 

 age ; that certain species of Oerithium live solitarily, and others 

 in society. 



He has likewise paid attention to the kind of nourishment 

 preferred by each species ; and if in this respect M. Dufo has 

 confirmed in a great measure Lamarck's division of the 

 Trachelipods into zoophagous and phytophagous, he has like- 

 wise removed some of the errors of that skilful zoologist. Thus, 

 according to him, the Cerithiums are exclusively phytophagous, 

 as well as the Cones and Cypi-seas, contrary to what Lamarck 

 supposed. 



Finally, it is not the same with regard to the mode and 

 celerity of locomotion in a considerable number of species ob- 

 served by M. Dufo. Thus the strombi and pterocerse advance 

 by what may be called successive bounds ; the cones are very 

 inactive, while it is otherwise with the Cyprseas, as might 

 have been anticipated from the gi-eat difference in the extent 

 of their locomotive disc. 



The considerable period (four years) during which M. Dufo 

 continued his observations, enabled him to judge of the dom- 



