ON GASTEROPODA. 395 
This has occasioned the species most common in great rivers 
to be called vivipara. This singularity was observed long 
ago among many species of ‘Turbo. 
There is nothing very peculiar in the manners and habits 
of the paludine. They generally live at the bottom of rivers, 
on the aquatic plants which are found there. They appear 
to feed on substances of all kinds, but more especially 
vegetable. Their mode of sexual intercourse offers nothing 
very worthy of remark. We have said that the young issue 
forth in a living state from the interior of the mother ; but they 
do not all come forth at once. The females of the paludinz 
appear to lay during the entire of the fine season. The little 
ones, on issuing forth, place themselves on the shell of the 
mother, and appear to remain there for some time. They 
crawl pretty fast on a resisting ground, and sometimes come to 
the surface of the water, where they can also float after the 
manner of the limnxz. ‘This, however, appears to take place 
very rarely. 
The species of paludine appear to exist only in our 
northern hemisphere, and not in the torrid zone, where they 
are replaced by the ampullarie. They seem to be very 
common in the rivers of North America. 
The JANTHIN constitute a very distinct genus, established 
by M. de Lamarck on a molluscous animal, which Linneus 
had classed with Henix. The name of Janthina indicates 
the colour of the handsome shell, which is a fine violet. ‘This 
genus has now been adopted by the generality of modern 
zoologists. 
The body of the animal is globular, as the form of the shell 
would indicate, and the visceral part is very small, compara- 
tively with the head, chest, and foot. The foot itself is not 
remarkably large, but it is very thick and muscular, and is dis- 
tinguished by a vesicular mass, which forms the principal 
characteristic of this animal. It is said to be a sort of sub- 
Aa2 
