458 



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 oeconomy 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. I 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- 

 rince with a shell ten times more ponderous in proportion 

 than the globular delicate lanthina, 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 lanthina is in the vici- 

 nity of Murex. It has been thought to approach Trochus ; 

 I am not of this opinion : 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 Muricidce. 



I therefore deposit lanthina as the first member of the new 

 family, forming, with the Eulimae and Chemnitzice, the passage 

 from the tribes with entire apertures to the Canalifera. The 

 aperture in lanthina, by its columellar elongation and canali- 

 ferous tendency, shows that it is in a state of transition, and 



