458 PELORID A. 
the organ is the membranous vehicle of the contents of the 
ovarium and matrix, that has descended from under the 
mantle, and fixed itself to the foot, for a very obvious purpose 
of the animal ceconomy in reference to the pulli in the genial 
season. It is probable, that as the animal, from its peculiar 
habitat, cannot, like the tribes of the coasts, deposit the 
germs of reproduction on marine substances, it makes use of 
the foot as a substitute, until its young emerge from the 
agglomerated mass of capsules to shift for themselves; then 
the temporary vesicular deposit is cast off. J have seen a 
similar appendage to the foot of the Pileopsis hungaricus and 
several other Gasteropoda. 
That this organ is not necessary for the floatation of the 
animal is strongly supported by the fact, that, as the sexes 
are distinct, many may be presumed to be males, and such 
often occur, without the so-called float. Many of the Litto- 
rine with a shell ten times more ponderous in proportion 
than the globular delicate Janthina, float with the shell 
beneath, and foot uppermost, in every direction, for days, 
without descending from the surface of the waters. 
It will be seen that the other parts of the animal scarcely 
differ from the more regular gasteropod. The double bran- 
chial plumes, one of them with two ranges of strands; the 
small head, the retractile, though short, inflated proboscis, 
and the rudimentary mucous fillets, which latter are only 
seen in the Canalifera, show that Janthina is im the vici- 
nity of Murex. It has been thought to approach Trochus ; 
I am not of this opmion: the above characters, with its 
oceanic habitat, food and habitudes, and absence of oper- 
culum, seem entirely to remove it from that genus, to which 
it would be difficult to find a colourable approach ; and above 
all, we may observe, that the illustrious Cuvier, by his dis- 
section, places it in the category of the Muricide. 
I therefore deposit Janthina as the first member of the new 
family, forming, with the Eulime and Chemnitzie, the passage 
from the tribes with entire apertures to the Canalifera. The 
aperture in Janthina, by its columellar elongation and canali- 
ferous tendency, shows that it is im a state of transition, and 
