332 NATICIDJE ; lANTHINID^ ; HALIOTIDvE. 



The Trochus longispina, from India, has the circumference orna- 

 mented with a row of long spines of a silvery or gold colour 

 placed at regular distances. 



998. The little family NATICID E, in which the shell is al- 

 most globular, is remarkable for having the front of the foot 

 dilated into a broad fold which conceals the head, and the lobes 

 of the mantle very large and covering a portion of the shell. 

 The animal is provided with a long retractile proboscis, and is 

 carnivorous in its habits. The species are all marine, and are 

 found in most parts of the world. 



999. The family IANTHINIDJE includes a few species of Mol- 

 lusca inhabiting a beautiful Snail-like shell, and from this cir- 

 cumstance, and the fine violet tint of the base of their shell, they 

 have received the name of Violet Snails. They are oceanic in 

 their habits, floating about freely in the open sea, where they 

 occur in vast numbers together, and are said to feed upon the 

 Velellce, which inhabit the same situations. When irritated 

 or alarmed, the lanthina pours out a violet secretion, which 

 darkens the water around it ; and thus serves for its concealment, 

 in the manner of the ink of the Cuttle-fish. But the most re- 

 markable circumstance in the history of this delicate and beau- 

 tiful creature, consists in its production of a peculiar float or raft, 

 composed of numerous cartilaginous vesicles filled with air, which 

 springs from the small foot in place of an operculum. To the 

 lower surface of this curious float the egg-capsules are attached, 

 and thus the lanthina carries its offspring about with it until 

 the young animals are fully formed. Nearly allied to these are 

 the HALIOTIDJE, of which the well-known Ear-shells are the 

 types. In this family the shell exhibits more or less of a spiral 

 structure, and there is a notch or perforation for the passage of 

 the anal siphon, which carries away the water from the bran- 

 chial cavity. The aperture is very wide, and there is no opercu- 

 lum. In the Haliotis, or Ear-shell, the shell is very flat and 

 slightly twisted at the apex, and within the convex margin there 

 is a series of perforations, of which those nearest the apex are 

 successively closed by shelly matter. This animal, in its living 

 state, is one of the most beautiful of Gasteropods, on account of 



