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analogue of an arboreal snail, whose organs and functions are fitted, by an 

 extreme modification of nature, to inhabit the sea. The beautifully reti- 

 culated lung of the air-breathing mollusk is transformed into a pectinate 

 gill for the respiration of water, the mouth is furnished with an armature 

 for the comminution of hard flesh-food of marine origin, less easily digested, 

 and to the foot is attached a broad dilated fin and vesicular float, contrived 

 for the purpose of sustaining the animal on the surface of the water. The 

 shell presents also the change that might be expected to result from its 

 difference of habit, being of a thin brittle calcined substance, and not en- 

 veloped by any of those hairy, or horny, or hydrophanous kinds of epidermis 

 which are peculiar to the plant-eating snail. 



The float of bubbles or vesicles, by which the Ianthince are more parti- 

 cularly distinguished, has been said to serve a mechanical purpose, by 

 which the animal is enabled to sink or swim at pleasure ; there does not, 

 however, appear to be any sufficient testimony to this effect, and it is diffi- 

 cult to imagine that such a use could be made of them ; but it has been 

 noticed that the Ianthince are rarely seen except in calm weather. According 

 to the observations of the eminent naturalists of the ' Voyage de T Astro- 

 labe/ the Ianthina deposit their ovaries, filled with minute eggs, in great 

 plenty about the vesicles, which the animal has the faculty of detaching. 

 Notwithstanding that few species are known, they are extremely prolific in 

 the equatorial seas, and, without doubt, as in the case of the surface-swim- 

 ming Pteropods, the predacious inhabiters of the deep allow them but a 

 limited existence. 



One remarkable peculiarity in Ianthina is, that in all the species, and 

 I believe six or eight will be found when they come to be examined, the 

 shell is of a uniform colour, a clear intense violet, and it is distinguished 

 more strongly, according to the species, by a close succession of extremely 

 delicate concentric lines of growth. The animal has been observed to 

 eject a violet fluid when alarmed or irritated. 



A considerable number of Ianthina were collected by Capt. Sir Edward 

 Belcher in the South Atlantic Ocean during the voyage of the Samarang,* 



* Mr. Arthur Adams, R.N., F.L.S., Assistant-Surgeon of the Samarang, has kindly favoured 

 Die with the following interesting observations made by him on this occasion. 



" In our passage from the Cape to St. Helena we experienced several days calm, the surface of 

 the South Atlantic being like a sheet of glass, and covered over with innumerable Ianthince, 

 Physalia, and Velella, with parties of Flying-fish and solitary Skip-jacks, emerging suddenly from 

 its depths and disturbing the stillness by their flights and splashings. In the act of swimming, 

 the dilated natatory appendages of Ianthina, are kept fully extended, while the vesicular float 

 precedes the shell, and keeps it in a reversed position on the surface" of the water. The female 

 evidently has the power of voluntarily detaching certain portions of the float to which any nidi- 

 mental sacks are fixed, for among the thousands obtained in the trawls, were several specimens 

 with hardly a remnant left, while isolated floats were also numerous. The high seas appear to 

 be the natural home of these beautiful mollusks, and I have seen a fleet of many hundreds 

 wrecked on the coral reefs of the Meia-co-shima Islands, making the shore quite blue at the water- 

 line. I have taken them up adhering in masses by means of the sucker-like fore-part of the 

 foot ; for although alive and uninjured, I never observed them make the slightest effort to crawl, 

 which mode of progression appears to be denied them. They have a habit, when nearly dead, of 



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