‘432 THE OCEAN WORLD. 
fleshy. It is this foot, which bears a vesiculous mass like foam, 
which gives its peculiar character to the pretty mollusc. The mass 
consists of a great number of small eggs, which 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 Ianthina inhabit the deep sea, and often form bands 
of very great extent. Messrs. Quoy and Gaimard have seen legions 
of Janthina 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 Janthina 
communis 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. 
Ffaliotis tuberculata, the ear-shell, is remarkable for its brilliant 
colours, and for a line of singular perforations in many of the species. 
The seventh family, Zurbinide, contains Zrochus, Turbo, Rotella, 
Monodonta, and Delphiniula. 
The species of the genus Zrochus 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 aseries 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 horny 
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 Zrochus 
niloticus (Fig. 218), Z: virgatus (Fig. 219), ZT: inermis (Fig. 220), and 
T. Cookit (Fig. 221), TZ: imbricatus (Fig. 222). 
The species of the genus 7uro are very generally diffused, being 
found on every shore, where they cling to rocks beaten by the waves. 
