Page:The Zoologist, 4th series, vol 4 (1900).djvu/339

Rh seaweeds, and is enabled, when displaced, to recover its previous position"; and we find it is stated by Jeffreys, for Rissoa generally, that the foot is grooved down the middle for about half its length towards the tail, whence it emits a glutinous thread, by which the animal suspends itself to foreign bodies or to the surface of the water. "Lying on a rock by the brink of a seaweed-covered pool left by the receding tide," says Jeffreys, writing of Rissoa parva, "it is no less pleasant than curious to watch the active little creature go through its different exercises—creeping, floating, and spinning." By "floating" the author means, evidently, creeping at the surface of the water, a habit which here, as in other molluscs, seems intimately associated with that of "spinning." The same naturalist mentions the latter habit in several other species: Rissoa membranacea, he says, "occasionally floats, or suspends itself by a viscous thread"; R. vitrea "suspends itself by a single byssal thread, keeping the mouth of the shell closed by the operculum"; R. abyssicola "floats like its congeners, and suspends itself in the water by a single byssal thread"; R. pulcherrima, exceedingly agile both in creeping and floating, "spins a delicate thread of attachment"; and the very tiny R.fulgida was frequently observed by the author "spinning a fine transparent slimy thread, and thus hanging suspended to a bit of seaweed or to the surface of the water." R. cancellata, Jeffreys further says, "is active and bold, floats like its congeners, and spins a byssal thread instantly on being detached from a crawling position"; R. carinata, moreover, like R. cancellata, "adheres with some tenacity to the stones on which it is found, and, when detached, it also spins a fine byssal thread, by means of which it suspends itself in the water." This last species, according to Mr. Brockton Tomlin's experience in the Channel Islands, is usually found under rather deeply-buried stones, to which it moors itself, he says, by a strong "byssus"; each individual, this observer obligingly tells the writer, had more than one short thread, generally, as far as he remembers, four or five. Barleeia rubra, according to Jeffreys, creeps at the surface, foot uppermost,