Gasteropoda.- 



-MOLLUSCA.- 



-lAi'THIXID^. 



333 



tliin and caducous, though in some of the northern 

 specifs it is thick, hard, and ptrsistcnt. The animals 

 of this family are chiefly inhabitants of sandy and 

 gravelly situations, ranging from low water to ninety 

 fathoms; either burrowing in the sand near the lowest 

 ebb of the tide, where their place of concealment is 

 indicated by a small heap of sand, or in sand-banl<s far 

 from sliore. Tliey are very voracious, not only boring 

 iiiio other shells by means of their elongate and 

 retractile proboscis, but, as Dr. Gould informs us, de- 

 vouring to a great extent the dead fish and other 

 animals thrown up by the tide. Tlie use of their large 

 foot is here obvious, for by expanding it they can 

 envelope completely the objects on which they prey. 

 They in their turn serve as food for fishes, being 

 devoured in great inmibers by the cod and haddock, in 

 the slomach of which animals they are often found. 

 The recent species are numerous, upwards of one 

 liundred having been described. They are widely 

 distributed, from the Arctic seas, through Britain and 

 the Mediterranean, to the Caspian ; and are found in 

 numbers in India, China, Australia, South Africa, and 

 the west coast of America, and the West Indies. 

 Some of the species, as Natica herculea, from Sitka 

 and tlie Oregon, attain a large size. The egg-cases of 

 the Natickhc are very curious; the spawn being 

 deposited in the form of a subspiral or concentric 

 ribband or strap, rendered firm b}' agglutinated sand. 

 Mr. Harvey descriljcs the nidus of a British species, 

 Natica {Neverila) monilifera, as firiii'.y gelatinous, or of 

 the consistence of gristle ; transparent or nearly so, 

 slightly coated with tine sand, and in shape resembling 

 the hoof of an animal. When dry, he says, they look 

 not unlike pieces of thin Scotch oat-cakes. The sur- 

 face is marked with little hexagonal spaces which 

 define the eggs. Dr. Gould in his " Invertebrata of 

 Massachusetts," describes a North American species as 

 a mass of sand glued together into the shape of a broad 

 bowl, open at the bottom and broken on one side. 

 The thickness, he says, is about that of an orange 

 peel, easily bent without breaking when damp, and 

 when held up to the light is seen to be filled with little 

 cells, arranged in quincunx order, each of these cells 

 containing a gelatinous egg with a yellow nucleus, 

 which is the embryo shell. In the collection of egg- 

 cases in the British Jluseum may be seen fine examples 

 of these nidi of British, North American, and South 

 African species. For a long time these curious pro- 

 ductions were considered by naturalists as zoophytes, 

 and descrilied under the names of Flustra armosa, 

 Escliura lutosa, &c. Ellis looked upon them as recep- 

 tacles for some sea insects. 



The opercula of the animals of the Kuticida, as we 

 have already stated, are eitiier horny or covered 

 externally with a coat of shelly matter. This difference 

 forms a good character for separating them into two 

 large groups, the Nuticina and Nereritina. The family 

 is represented in Plate 1, figs. 1-3, by Slomatia halio- 

 loiileum, and fig. 4, Natica millepunctata. 



Passing the family Neritopsida, the animals of which 

 are unknown, and the species very few in number, we 

 come to two larger and more interesting families ; 

 these are the Violet Snails and the Wentle-traps. 



Family— lANTHINID^E [The Violet Snails). 



This family contains only one genus, laittliina. The 

 animals belonging to it have a small flat foot whicli is 

 furnished with a vesicular appendage on its hinder part, 

 on the underside, which serves an important purpose. 

 The shell is thin, translucent, and spiral, with a very 

 small, sinistral nucleus. It resembles in shape that of a 

 Helix, but is of a close vitreous texture. The aperture 

 is large, somewhat quadrangular, with a strongly- 

 twisted columella, and a thin, sharp outer lip, notched 

 at the outer angle. The species all partake, more or 

 less deeply, of a violet hue — hence the name of the 

 genus. The animals appear to be quite blind, having 

 eye pedicels at the base of the tentacles, but no trace 

 of eyes. As they seem, however, to select the night 

 for their predatory operations on the high seas, this 

 deprivation can be of little moment to them. They 

 are pelagic, that is, they are found floating about on 

 the surface of the ocean, often in myriads, and appar- 

 ently always gregarious. The apparatus by which 

 they keep themselves constantly at the surface consists 

 of the vesicular appendage to the foot mentioned above. 

 This float, as it is called, is composed of numerous 

 cartilaginous air-vesicles, and was aptly called by 

 Fabius Columna, the first describer of the lanthina, 

 Spuma Cardlaginea ; the vesicles, says Dr. Johnston, 

 being as transparent as the air-bubbles in foam, while 

 the skin is cartilaginous. " Buoyed up on these air- 

 bladders, the lanthina floats at ease, not left, however, 

 to be driven at random by every current or breeze 

 which may sweep across its path, for its course is 

 guided by means of a small fin wliich runs along each 

 side of the foot, a little above its edge. It is oidy when 

 the ' tempest's breath ' blows hard that the snail yields 

 to its violence, and suffers wreck on the unfriendly 

 shore." — {Johnston.) This curious float is entirely 

 secreted by the foot, and it has been found that when 

 a portion is removed the injury is rapidly repaired. 

 In addition to the use of this appendage as a float, it 

 has been ascertained that the animal attaches its egg 

 capsules to its under surface, suspending them there by 

 little pedicels. It occupies a considerable time in the 

 deposition of these eggs, and the capsules nearest to 

 the extremity of the float are constantly found empty. 

 The central ones contitin young shells fully formed, 

 and those nearest the animal are filled with eggs, "and 

 it appears probable," says Dr. Coates of Philadelphia, 

 who has had opportunities of observing these creatures, 

 " that the young animals, when liberated from their 

 chambers, ascend the float of the mother, and in this 

 way gain access to the surface." By some naturalists 

 this float is considered to be an extreme modification 

 of the operculum. It is much too large to be with- 

 drawn into the shell, though some writers have sup- 

 posed that the animal has the power of compressing it 

 in such a manner as to make the shell sufficiently 

 heavy to sink. All recent observers, however, assure 

 us that tliese creatures iiave no power of sinking in tlie 

 water. Dr. Bennett found on purposely irritating the 

 animal, or even touching it in ever so slight a degree, 

 that it withdrew itself within the shell, but had no 



