Other very elegant species are Patella umbella (Fig. 213), from the African coast. Patella granatina (Fig. 214), the ruby-eyed Limpet from the Antilles; Patella barbata, the bearded Limpet (Fig. 215); and the long spined Limpet, Patella longicosta (Figs. 216 and 217).
Figs. 216 and 217. Patella longicosta (Lamarck).
The fourth family, Calyptræidæ, types Pileopsis and Calyptræa, was classed by the older conchologists with Patella. Pileopsis Hungaricus, the Hungarian bonnet shell, is rather abundant on some parts of the British coast.
The fifth family, Fissurellidæ, contains Parmophorus, the duck's-bill-limpet of Australia, and Fissurella, the key-hole-limpet, which is remarkable for the opening of the apex of the shell.
The sixth family, Haliotidæ, contains Ianthina, Scissurella, and Haliotis.
Fig. 218. Ianthina communis
(Lamarck).
The attention of naturalists has long been directed to a curious mollusc known under the name of Ianthina communis (Fig. 218); its body is globular, and it presents an opening in front without contracting itself in order to form the head, which is long and trumpet-shaped, terminating in a large buccal opening, furnished with horny plates, and covered with little hooks; and two conical tentacles, slightly contracted, but very distinct, each bearing at their external base a long peduncle. The foot is short, oval, divided into two parts: the anterior, concave and cup-shaped; the posterior, flat and 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 bladders, which combine to keep the animal on the surface of the water. The shell is light, transparent, violet-coloured, and very much resembles the shell of the Helix. The Ianthinas inhabit the deep sea, and often form bands of very great extent. Messrs. Quoy and Gaimard have seen legions of Ianthinas driven by the current. They have sailed during many days through these wandering tribes, which would be the sport of every gale if they could not, by drawing their heads within their shells and contracting their natatorial vesicles, 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 Ianthina 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.