like the Rissoæ, and occasionally secretes a slight mucous filament, by which it suspends itself from the surface of the water or from seaweeds.[1]
Hydrobiidæ.
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.[2] 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;[3] 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.
Skeneidæ.
Skenea planorbis, according to Jeffreys, "occasionally suspends itself in the water by spinning a viscous thread with its foot."[4]
Jeffreysiidæ.
Jeffreysia diaphana, also, according to the same author, "spins a slimy suspensile thread."[5]
Litiopidæ.
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
