432 THE OCEAN IVOIil.D. 



fleshy. It is this foot, wliich hears a vesiculous mass like foam, 

 which gives its peculiar character to the pretty mollusc. I'he mass 

 consists of a great number of small eggs, wliich help to keep 

 the animal on the surface of the water. The shell is light, trans- 

 parent, violet-coloured, and very much resembles the shell of the 

 Helix. The lanthina inhabit the deep sea, and often form bands 

 of very great extent. ]\Iessrs. Quoy and Gaimard have seen legions 

 of lanthina driven by the current. They have sailed during many 

 days through these wandering tribes of molluscs, which would be the 

 sport of every gale if they could not, by drawing their heads within 

 their shells and contracting themselves, diminish their volume 

 and increase their weight at- will, so as to sink quietly to the 

 bottom of the water till the tempest was over. The lanthina 

 coinmunis possesses a liquid of a dark violet colour, which is believed 

 by many naturalists to have been one of the purple dyes known to 

 the ancients, if not the purple of Tyre : it is very common in the 

 Mediterranean, and in all the oceans. 



Haliotis tubcrailata, the ear-shell, is remarkable for its brilliant 

 colours, and for a line of singular perforations in many of the species. 



The seventh famil}^, Turlunida;, contains Troc/nis, Turbo, Rotella, 

 Alonodonla, and Dclphinula. 



The species of the genus TrocJius are found in all seas, and near 

 to the shore in the clefts of rocks, especially in places where sea- 

 weeds grow luxuriantly. Some of these thick, cone-shaped shells 

 are extremely beautiful, being richly nacred inside, and often re- 

 markable for the beauty and diversity of colour they exhibit. 

 Generally smooth, the principal spiral is, nevertheless, sometimes 

 edged with a series of regular spines. The form is conical, the spiral 

 more or less raised, broad and angular at the base ; the opening 

 entire, depressed transversely, and the edge disunited in the upper 

 part. 



The animal which inhabits this shell is also spiral ; its head is 

 furnished with two conical tentacles, having at their base eyes borne 

 on a peduncle ; its foot is short, round at its two extremities, edged 

 or fringed round its circumference, and furnished with a horn}' 

 operculum, circular and regularly spiral. 



The family consists of many genera or sub-genera. Among the 

 species of Trochus, properly so called, we may notice TrocJnis 

 niloticus (Fig. 2x8), T. virgatiis (Fig. 219), T. mermis (Fig. 220), and 

 T. Cooldi {Y\g. 221), T. inibrkatus {Y\g. 222). 



The species of the genus lurbo are very generally diffused, being 

 found on every shore, where they cling to rocks beaten by the waves. 



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