98 Molluscs of the isles Sechelles and Amirantes. 



are not without interest, because they unite certain links 

 in the natural history of molluscous creatures. 



Thus the depth and nature of the bottom of the sea which 

 the different species of shell-fish prefer, have been carefully 

 noted by M. Dufo. He has remarked, for example, that 

 the Bivalved sabulicolte descend deeper as they become more 

 aged, that certain species of Cerithia live solitary, and others 

 in society. 



He was equally occupied in investigating the variety of 

 nutritive matter preferred by each species ; and if after 

 this manner, M. Dufo in a great measure has confirmed 

 the division of M. de Lamarck, viz. Trachelipoda, Zoophaga 

 and Phytophaga, he was also enabled to point out certain 

 errors committed by that learned zoologist. Thus accord- 

 ing to him the Cerithia are exclusively phytophagous, as 

 well as the Conus, and the Cypraea, in contradiction to 

 what M. de Lamarck had supposed. 



In fine, M. Dufo has gone so far as to observe the manner 

 and velocity of locomotion of a great number of species ; thus 

 the Strombi and the Pterocerae progress by successive skips 

 as it were, and the Coni are slow in comparison with the 

 (Porcelaines) Cypraeae, which we might presuppose from the 

 great difference in the extent of their locomotive disk. 



The time (four years) during which M. Dufo continued his 

 observations, permitted him to judge of the length of life of 

 certain species by the slowness of their development. It 

 is on the Cerithium palustre that this presumption essentially 

 bears. Among the peculiarities which it would be difficult 

 to unite with those already mentioned, we shall intimate 

 the following : The Buccinum arcularia, the operculum of 

 which is finely denticulated at its circumference, seems to 

 serve as a means of defence when we wish to capture it. 



The double foot of the Harpae, first made known by M. 

 Quoy, to whom science owes such a number of new facts in 

 Malacology and Actinology, and which appears to replace 



