Mollmcs of the isles Sechelles and Amir antes. 99 



the operculum of which this genus is deprived, falls and 

 breaks with the least effort, and seems thus a means which 

 the creature has to avoid the verocity of its enemies in aban- 

 doning to them this part of its body. 



In the (Cypraese) the lobes of the mantle are in a singular 

 state of continual trepidation, which does not take place in 

 the (Olivae), a genus which is so nearly allied to the Cypraese. 



The air-bearing vescicules of the foot of Ianthinus empty 

 themselves entirely when the creature is at certain depths 

 in the sea. 



The Agathinus of Maurice deposits its eggs in columns, 

 forming a train more or less long, but the fact the most 

 remarkable of this genus which M. Dufo has observed is, 

 that the Helices unidentes are oviparous, like many species of 

 Littorinae, the Paludina Vivipara of our rivers, the Partul 

 &c. that is to say they hatch their eggs in the extremity 

 of their oviduct, and the little creature leaves its parent 

 in a living state. 



Certain species of Calyptrse are provided with a support 

 distinct from the rock on which this creature is placed, while 

 in the Hipponices vivantes, the support makes part of the 

 rock, and is formed at its surface. In fine, M. Dufo appears 

 to be assured that certain byssifirous bivalve creatures detach 

 (the byssus piecemeal), which we had already suspected. 



In limiting ourselves to this simple enumeration of facts 

 gleaned by M. Dufo, it will be permitted us to add that if, 

 among the truly immense number of shells collected by 

 M. Dufo we shall only find forty or fifty new ones, a conse- 

 quence which, although simple, is however generally more 

 appreciated for our collections, he has furnished us on the 

 species which we already know peculiarities which will 

 certainly advance their history, and which was much more 

 difficult to procure. 



In fact, to accomplish this, it was necessary to do some- 

 thing other than amass and collect these creatures, and to 



