Naticse, Lamellarise, and Velutinse. 47 



mighty waters of the Atlantic and Pacific ; the various species 

 are occasionally wafted to the diiFerent shores of the world. 

 More than twenty years ago, many of the lanthina communis 

 were brought to us alive, though collapsed, collected on the 

 South Devon coasts ; I believe none have appeared since in those 

 localities. 



This genus has long caused embarrassment to naturalists, and 

 is still a source of difficulty in regard to the structure of the 

 animal and its natural position ; but I think the obstacles to a 

 true determination will disappear on attentive consideration. The 

 great stumbling-block is the float, as it is called, or vesicular 

 mass attached to the foot, which has been considered an hydro- 

 static apparatus. This idea is erroneous : the organ is the mem- 

 branous 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 oecouomy 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 Imngaricus and 

 several other Gasteropoda. 



That this organ is not necessary for the floatation of the animal 

 is strongly supported by the fact, as the sexes are distinct, that 

 many may be presumed the males, and such often occur without 

 the so-called float. Many of the Littorince with a shell ten times 

 more ponderous in proportion than the globular delicate lanthina, 

 float with the shell beneath, and foot uppermost, in every direc- 

 tion 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 branchial 

 plumes, one of them with two ranges of strands ; the small head, 

 and the retractile, though short, inflated proboscis ; and the ru- 

 dimentary mucous fillets, which latter are only seen in the 

 Canalifera, show that lanthina is in the vicinity 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 operculum, 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 Muricida. 



I therefore deposit lanthina as the first member of the new 

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

 from the tribes with entire apertures to the Canalifera : the 



