Page:The Zoologist, 4th series, vol 4 (1900).djvu/350

320 specimens in a basin of sea-water, observed that they crawled to the edge and suspended themselves by a thread.

—A Water-Snail (Limnæa auricularia) hanging by a thread from the surface of the water in an aquarium. After Taylor, 'Monograph of the Land and Freshwater Mollusca of the British Isles,' i. (1899), p. 318 (fig. 610).

—A fresh-water Limpet (Ancylus lacustris) using a thread. From a sketch by Prof. Cockerell.

—Diagram illustrating the use of threads by aquatic Pulmonate Molluscs, based for the most part on observations recorded for Physa hypnorum, by Mr. G.S. Tye. The animal is ordinarily slightly lighter than water:— an individual crawling through the water towards the surface, leaving its locomotory mucus behind in the form of a thread, which retains the animal, and prevents its sudden rise to the surface; the animal at the surface, taking in a supply of air—the thread, having been continued as a floating slime-trail, is now attached to the surface;  the animal returning by descending its thread; another individual is making use of the fixed thread for ascent. An upward journey may be abandoned, the animal in that case returning upon its unattached thread,

—"Megalomastoma suspensum," a land operculate of doubtful identity, at rest, suspended by a number of threads from a twig; probably much enlarged. After Swainson, 'Treatise on Malacology,' 1840, fig. 29; presumably from a sketch by Guilding.

—Chondropoma dentatum, a land operculate, at rest, suspended by a short thread; slightly enlarged. After Binney, 'Terrestrial Air-breathing Mollusks of the United States,' ii. (1851), p. 347.

—Cerithidea obtusa, a brackish-water, somewhat amphibious, operculate mollusc, at rest, suspended to a bough by a number of short threads. After A. Adams, 'Zoology of the Voyage of H.M.S. Samarang: Mollusca,' 1848, pi. xiii. fig. 3 b.