GASTROPODS. 



33i 



on the contrary, the number of laterals occasionally reaches live a side. 

 are curved and claw -like in some groups, but in others merely have serrated 

 edges. Forty-two families are included in this section; but the limits of this 

 work admit only of an account of some of the more important. The animals of 

 one group are provided with shells, which either have a distinct, prolonged 

 anterior canal, or else the aperture is more or less deeply notched at the base. In 

 another group the mouth is entire, without notch or siphonal canal. Some have a 

 retractile proboscis, like murices and whelks ; others have a longer or shorter 

 muzzle or rostrum, which is somewhat contractile. 



The first family is that of the tritons (Tritonidce), many of which possess large, 

 handsome shells, exhibiting strengthening ridges (or former lips) at intervals upon 

 the spire. The animal has a shortish foot, a large head projecting between the 

 slender, pointed tentacles, supporting the eyes at the sides or at the base, and a 

 horny operculum. Triton and Ranella are the two genera constituting this 

 family. In the former, the large T. tritonis, the war-trumpet of the South-Sea 

 islanders, is the typical kind. It attains more than a foot in length ; and when 

 the top of the spire is broken or ground off, a booming note can be produced. 

 A similar species (T. nodiferus) lives in the Mediterranean, and was employed in 

 the same way by the Komans. Most of the tritons are covered with a conspicuous 

 periostracum, and in some cases this is beset with short hairs or bristles. The form 

 of the shells is very variable in the different subgenera, but all exhibit the 

 character of periodic ridges. The shells in the genus Ranella are very like Triton ; 

 but the typical forms possess a posterior canal or sinus at the upper part of the 

 aperture, which is not met with in the latter. The varices are mostly in two 

 continuous series, one up each side of the sjnre. The species of this and the 

 preceding genus are not very numerous — hardly two hundred altogether — and are 

 chiefly inhabitants of warm climates. A few range as far north as Alaska and 

 Japan ; others occur on the shores of Patagonia, the Cape of Good Hope, Amsterdam 



Island, and New Zea- 



land. Two species — Ufl 

 T nodiferus and T. 

 cutacens — have been 

 occasionally obtained 

 from the Channel 

 Islands. Like Strom- 

 bus, this group of 

 molluscs appear to 

 be great scavengers. 

 M. Velain, when at 

 Amsterdam Island, 

 observed that the 

 dead carcases of seals, 

 left by fishermen on 

 the rocks at low 



water, were literally covered with lobsters and RdTiMa at the following tide In 

 the helmet-shells, family Cassididce, the shells develop varices at intervals, like 



HELMET-SHELL [CdSSis gluuca). 



