PULMONARY GASTEROPODS. 413 



The fifth family, Fissurellidse, 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, Haliotidse, contains lanthina, Scissurella, and 

 Hatiotis. 



The attention of naturalists has long been directed to a curious 

 mollusc known under the name of lantliina communis (Fig. 218) ; 

 its body is globular, and it presents an opening in front without con- 

 tracting 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 



' Fig. 218. lantliitia communis 



long peduncle. The foot is short, oval, divided (Lamarck), 



into two parts : the anterior, concave and cupshaped ; 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 

 lanthinas inhabit the deep sea, and often form bands of very great 

 extent. Messrs. Quoy and Gaimard have seen legions of lanthinas 

 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 lanthina 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. 



Haliotis, the ear-shell, is remarkable for its brilliant colours, and 

 for a line of singular perforations in many of the species. 



The seventh family, Turbinidte, contains Trochus, Turbo, ProteUa, 

 Monodonta, and DelpJiinula. 



The genus Trochus are found in all seas, and near to the shore in 

 the clefts of rocks, especially in places where seaweeds grow luxuri- 



