64 



SHELLS AND SHELL-FISH. 



PART I. 



This and Ranella appear to be the two typical genera ; 

 but of the three aberrant divisions^ Triton is the only 

 one that has been yet named or defined. The foliated 

 varices of Ranella, and the sharp tubercles on the whole 

 shell, joined to the additional canal at the upper part of 

 the aperture, indicate that this group is naturally con- 

 nected to Miirex ; but the species are very few, and 

 , present no very marked deviation from the typical form. 

 In Triton, however, the case is far otherwise. The 

 species are not only more numerous, but exhibit in their 

 structure so many different modifications, that there is no 

 one generic character to which there are not exceptions 

 in some of the species. The most usual is that of having 

 but few varices, and these placed alternately ; whereas 

 in Ranella they are so united as to form a continuous 

 ridge on each side the shell, when it is placed with the 

 aperture downwards. But this character is by no means 

 constant. The animal {fig. 1.) is here represented from 



an unpublished drawing by Guilding ; the tentacula 

 are short, and the eyes at their base. This remarkable 

 diversity in the genus Triton is easily accounted for, on 

 the ground that this group contains representations of 

 all others in the family, besides aberrant forms leading 

 to the more proximate genera. The two other aber- 

 rant types, which we consider as completing the circle 

 of the Muricince, we name Vitulina and Muricidea. 

 The first is advancing towards Murex, and is repre- 

 sented by the Mureoc Vitulinus of authors, and is dis- 

 tinguished by having the varices nearly obsolete, and 

 the piJlar smooth, broad, and flattened, like a purpura. 



