Page:The Zoologist, 4th series, vol 4 (1900).djvu/322

292 These little Snails, as far as the writer has ascertained, are the only Helicoid-shelled molluscs known to make threads; the Trochonanina conula was collected by Garrett from foliage of bushes in the Cook's or Harvey Islands, and in the Society Islands.

There is a statement in Mr. Tye's "Molluscan Threads" (1878) that Mr. Dixon, of Leeds, "has seen several individuals of Clausilia rugosa var. dubia suspended." A number of Clausilia rugosa kept by the present writer for a considerable time in glass vessels, with twigs, &c, were not seen, however, to use a thread; and, as indicated above, two other species of Clausilia have been experimented with on twigs of needle-furze with similar negative results. Clausilia rugosa, it is true, was sometimes seen hanging during rest by a point of dried mucus, attaching the lip of the shell to the object of support, and allowing the creature to swing freely; but this, apparently, was merely the result of the breaking away or failure of the greater part of the film by which resting Clausiliæ ordinarily fix the mouth of the shell; a method of attachment familiar to us in the common Snails (Helix, &c). In Helix (and probably in Clausilia also) the mucus of this attachment comes, not from the foot, but from the mantle. On inquiring of Mr. Dixon, in 1893, the writer found that the observation on Clausilia had passed from his memory; he stated, however, that he had seen Balea perversa, in the Isle of Man, suspended by a string of mucus about an inch long from the under side of stone ledges; he supposed that the animals, in crawling over the ledges, had overbalanced, and that their mucus, more glutinous than usual owing to the dry weather prevailing at the time, had held them suspended, and had been gradually drawn out by the weight of the mollusc.

The air-breathing fresh-water Snails of this and the next family are notorious spinners, the habit being associated with the visits to the surface of the water which most of these creatures are compelled to make from time to time for the purposes of respiration. Most of them have light shells, and when