Page:The Zoologist, 4th series, vol 4 (1900).djvu/340

310 like the Rissoæ, and occasionally secretes a slight mucous filament, by which it suspends itself from the surface of the water or from seaweeds.

Lindström (1868) has referred to the spinning of a mucus-thread (by which the animal, with half-closed operculum, keeps itself suspended from the water-plants) as a character, among others, tending to associate the fresh-water Bythiniæ with the estuarine Hydrobiids. Bythinia, now always regarded as a Hydrobiid, is certainly a spinner, Mr. Tye having seen Bythinia tentaculata suspend itself, usually after "floating," the thread being attached to the surface of the water; but the writer is not acquainted with observations on other members of the family. In 1894 I kept several specimens of Hydrobia ulvæ and one of H. ventrosa under observation for ten days, in a vessel of water with weed, &c.; they often "floated" (crept at the surface of the water), but were not seen to suspend themselves.

Skenea planorbis, according to Jeffreys, "occasionally suspends itself in the water by spinning a viscous thread with its foot."

Jeffreysia diaphana, also, according to the same author, "spins a slimy suspensile thread."

Litiopa melanostoma, a small, more or less Rissoa-like creature (less than a quarter of an inch in length of shell), an inhabitant of the gulf-weed of the mid-Atlantic (Sargasso Sea), is perhaps the most notorious of all the spinning molluscs. Its history is briefly as follows: —

(1). Bélanger discovered the creature in 1826, and made a number of observations on its habits; and, on his return to France, read his notes to Rang, at the same time handing him