FRONT-GILLED GROUP 



3351 



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 Romans. 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 characteristic 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 spire. The species of this and the preceding genus 

 are not very numerous hardlj" two hundred altogether and are chiefly inhabit- 

 ants 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 

 T. nodiferus and T. 

 cutaceus have been 

 occasionally obtained 

 from the Channel 

 islands. Like Strom- 

 bus, this group of 

 mollusks appear to 

 be great scavengers. 

 M. Velain, when at 

 Amsterdam island, 

 observed that the 

 dead carcasses of seals, 

 left by fishermen on 

 the rocks at low 



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

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

 tritons, but they are broader, more globose, and have shorter spires. The aperture 

 is more or less dentate on each side, and the siphonal canal short, and sharply 

 recurved. Upon the columellar side the animal deposits a strong shelly callosity, 

 which in some species is enormous, and unites with the outer lip above. The 

 animal closely resembles that of Triton; its dentition is similar, but the opercula in 

 this family are peculiar, having a lateral nucleus, and often being rayed like an 

 expanded fan. The shells of some species consist of different-colored layers, and 

 are made use of for carving shell cameos, in order that the subject may stand out 



HELMET SHEI.I, (Cassis glauca). 



