96 



tlie faculty of suspending the function of its calcifying organ at different 

 intervals in the course of its growth, at the same particular periods in each 

 species, in a manner exactly similar to that which induces the formation of 

 claws just described in the mature Pterocera. In that genus there is no 

 appearance of this defensive architectural border until the animal is engaged 

 in the completion of its edifice, a natural effort for the attainment of that 

 symmetry and finish by which the works of the Inxdsible are characterized ; 

 but in the Tritons, Mandla, and Murices, it occurs at a very early stage of 

 growth, the even teuour of the shell is renewed, and the varix is repeated 

 at successive intervals. In Miirex there are three or more in every whorl ; 

 in Ranella, one in every half-whorl ; whilst in Triton, the periodical deve- 

 lopement of a varix occurs less than twice in a whorl, the genus in- 

 cluding, not only those having a varix in every whorl, but those in which 

 a varix occurs on the last whorl only. Some species are found occasionally 

 without any varix at all, but this is merely a fortuitous variation of growth. 



Such is the arrangement of the varicose Canalifcra in popular use; 

 several genera have been proposed for further subdividing them, the most 

 plausible of which is the genus Fersona of De Montford, for the Triton es 

 aims, mnlas, &c.; whilst Dr. Pfeiff'er, on the other hand, unites ihaBaneUfC 

 and Tritons into one. All were included by Linnseus under the head of 

 Murex, and there is little or no difl'erence of generic value in the soft parts ; 

 it has been observed, however, by M. Deshayes, that the animals of the 

 different species of Triton, excepting the great Trumpet shell* {Triton 

 ■variegatus), and one or two large allied species, are distinguished by an 

 occellated pattern of colouring as in the T. tuberosits here figured. 



The Tritons have shells of more solid structure than the Murices or 

 Ranella, and of more simple gro\vth. They are not furnished with fronds 

 or spines, nor have they any ramified branches like the Murices ; the rude 

 manner in which the whorls are convoluted seems rather to indicate that 

 their animal inhabitant, though possessing abundant power of calcification, 

 is of somewhat sluggish growth. The epidermis of the Tritons is often 

 remarkably thick, hairy, and bristly, and is sometimes accompanied witli 

 bristles in small tufts. Another curious peculiarity in these shells is the 

 structure of the apex ; it appears in numerous instances to be formed of 

 a horny substance, thinly plated with shelly matter, and it is not an uncommon 

 thing to find examples in which the calcareous plating is broken off so as to 

 expose the horny cast underneath. The columella, of the Tritons is gene- 



* 111 the early ages of Greece, it was customary for the Krjpv^, or comnion crier, to introduce 

 himself to the notice of the people by lustily blowing through a shell. We learn from tradition, 

 as well as histoiy, that the Triton variegatus or Trumpet-Shell {Mtirex Tritonls, Linn.) was the 

 one commonly selected for that purpose ; but it is more probable that the shells of many other 

 CanaJifcra were used. Be that as it may, it is certain that the word Kerix was applied by 

 Aristotle from that circumstance to all the canaliculated shells with which he was acquainted, and 

 it appears to have passed by a strange process of conaipliuu, into that of Miire.r. — Conch. 8i/si. 

 vol. ii. p. 191. 



