392 MOLLUSCS, 



shell. The most interesting feature in connection with these oceanic snails is the 

 curious float which they construct to support their egg-capsules. It is a sort of 

 gelatinous raft, enclosing air-bubbles which cause it to float at the surface ; and is 

 attached to the foot, the egg-capsules being suspended from its under surface. The 

 violet-snails feed on various kinds of jelly-fish, and occur in shoals on the high seas. 

 Being unable to sink, so long as they are in connection with their floats, they thus 

 escape from storms and are often cast ashore in immense numbers. The species 

 are few, and, like other pelagic forms, are widely distributed. Reduzia, the only 

 other genus in the family, has a pale brownish shell with a longer spire than 

 lanthina. It likewise forms a raft. The shells of the wentle-traps (Scalariidce) 

 are mostly white, and formed on the same pfan. The spire is more or less 

 elevated, the aperture entire, and the whorls are ornamented with a succession 

 of ribs or varices which give the shells a pretty appearance. The animals are 

 carnivorous. More than one hundred and fifty species are known, and they occur 

 in all seas, as far north as Greenland. Four inhabit the British shores, one 

 (Scalaria communis) being the most prettily coloured shell of the genus. S. 

 pretiosa, a native of the China Seas, is the largest member. It was formerly 

 of value, between twenty and thirty pounds having been given for a specimen. 



SECTION GYMNOGLOSSA. 



This, the last of the five sections into which the Pectinibranchs are divided, 

 is characterised by the absence of the radula. Two families are included in it, 

 namely, the EulimidcB and Pyramidellidce. The former have white, polished, 

 pointed shells, with an ovate aperture, closed by a thin, horny operculum. Many 

 of them are curved in the course of growth. Some are known to live commensally 

 or parasitically upon or within various species of holothurians. Stylifer, which 

 lives in or upon star-fish and sea-urchins, usually has a thinner and more glassy 

 shell than Eulima, and has no operculum. A few species are found in Britain, 

 but the family is more numerous in warmer latitudes. In the second family the 

 majority of the species are very small; and while all are dextral in the. adult state, 

 the young shells are remarkable for having the nuclear whorls sinistral. Some are 

 longitudinally plicate, others transversely ridged, cancellated, or smooth, and the 

 columella often exhibits one or more plaits or denticles, which are conspicuous in 

 some and almost obsolete in others. The diversity of form and surface ornamenta- 

 tion, in the very numerous species of this and many other families, can only be 

 seen in a collection of specimens, or a good series of illustrations. About forty 

 species are British, none of which belong to the typical Pyramidella. 



Suborder Heteropoda. 



This group is regarded by some systematists as a distinct order, and by others 

 merely as a division of the Pectinibranchia ; and it sometimes appears under the 

 name of Nucleobranchiata. It includes gastropods modified for a pelagic life. 

 The foot, in place of being adapted for crawling, is laterally compressed, and serves 

 the purpose of a fin, and is also used as a means of attachment to the prey or any 

 floating substances. The Heteropods are found on the high seas in every warm 

 part of the globe. They have distinct sexes, are predatory in their habits, feeding 



