68 M. Dufo on the Mollusca of the 



tion of the life of some of the species by the slowness of their 

 development. This presumption refers more particularly to 

 Cerithium palustre. 



Among the peculiarities which it would be difficult to class 

 under any of the above heads, we may mention the following : 



Buccinum arcularia has its operculum finely denticulated 

 round the edges, and this it seems inclined to use as a defence 

 when one is about to seize it. 



The double foot of the Harpse (first noticed by M. Quoy, to 

 whom the science is indebted for a great number of new facts 

 in malacology), which appears to replace the operculum, want- 

 ing in this genus, falls and breaks on the slightest effort, and 

 thus seems to afibrd the animal a means of escape from the vo- 

 racity of its enemies, by leaving to them this part of its body. 



In the Cyprseas, the lobes of the mantle are in a singular 

 state of continual vibration, which does not take place in those 

 of the Ovula, a genus so nearly allied to the Cyprsea. 



The aeriferous vesicles in the foot of the Janthinse are 

 completely empty when the animal is at a certain depth in the 

 sea. 



The Achatina ma ritiana deposits its eggs in a column form- 

 ing a train of some length ; but the most remarkable fact of 

 this kind observed by M. Dufo, is, that certain Helices are 

 ovoviviparous, like several species of Littorina, the Paludina 

 mmpara of our rivers, the Partulas, &;c. : that is to say, that 

 the eggs are evolved in the end of the oviduct, and the young 

 issue from the mother in a living state. 



Some species of Calyptrsea are provided with a support dis- 

 tinct from the rock on which the animal rests, while among the 

 living Hipponices, the support forms part of the rock, and is 

 hollowed on the surface. 



Finally, M. Dufo seems to have ascertained that certain 

 bivalves, provided with a byssus, detach their byssus piece by 

 piece, as was previously conjectured. 



While limiting ourselves to this simple enumeration of the 

 principal facts determined by M. Dufo, we may be permitted 

 to add, that if, among the truly immense number of shells 

 which M. Dufo has brought with him, we find only forty or 

 fifty new species, — which are both more easily obtained, and 



