weaken the base that it is unable to support the weight of the frond, and thus the plant is detached and driven on shore by the waves. [Illustration: Limpet and Shell.] The beautiful Sea-ear, or Haliotis, is the chief representative of the scutibranchiate gasteropods. The flattened shell, perforated with small holes on one side, is characterised by a very wide mouth or aperture, the largest in any shell except the limpet. The outside is generally rough, or covered with marine substances; the inside presents the same enamelled appearance as mother-of-pearl, and exhibits the most beautiful colours. The holes with which the shell is perforated serve to admit water to the branchiæ, and are formed at regular intervals as it increases in size. The foot is very large, having the margin fringed all round, and is able, like that of the chiton or the limpet, to cling firmly to the rock. More than seventy species of Haliotis are known, the greater part occurring in the Pacific Ocean. [Illustration: Haliotis. _c._ Series of perforations. _d._ Eye peduncles. _e._ Tentacles. _g._ Foot. ] [Illustration: Carinaria.] To the scutibranchiate gasteropods also belong the strangely formed Carinariæ, which seem to be made up of disjointed parts. The gills (_g_) project from under a thin vitreous shell (_f_), which projects from the dorsal surface, and has a form not unlike that of the Argonaut or of a Phrygian cap. The foot (_b_) is not formed for creeping, but constitutes a muscular vertical paddle or fin, that serves them for swimming on the back, and is furnished with a sucking disk (_c_), with which they are enabled to attach themselves to floating objects. The Pectinibranchiata comprise all the spiral univalve shells, and are by far the most numerous of all the gasteropods, as their species are not counted by hundreds, but by thousands. If their calcareous garment could be drawn out, it would be found to consist of a tube gradually widening from the apex to the base; but what an immense variety of form and ornaments, what a prodigality of splendid tints, has not Nature spread over this interminable host! The same fundamental idea appears to us in thousands of modifications, one yet more elegant and capricious than the other. Thus the passion of the shell collector is as conceivable as that of the lover of choice flowers, and when we read that rich tulip-amateurs have given thousands of florins for one single bulb, we cannot wonder that many of the Volutes, Cones, Mitres, and Harps, are worth several times their weight in gold; that more than a hundred pounds have been paid for a Chinese wentle-trap, and that the _Cypræa aurora_, which the Polynesian chiefs used to wear about the neck, is valued at thirty or forty guineas. [Illustration: Orange Cone-Shell.] [Illustration: Mitre-Shells.] [Illustration: Harp-shell.]