310 THE ZOOLOGIST. 



like the Rissoce, and occasionally secretes a slight mucous filament, 



by which it suspends itself from the surface of the water or from 



seaweeds.* 



Hydrobiid^. 



Lindstrom (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 Bythinice with the 

 estuarine Hydrobiids.t Bytliinia i 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 ;I but the writer is not 

 acquainted with observations on other members of the family. 

 In 1894 I kept several specimens of Hydrobia ulvce 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. 



Skeneid^. 

 Skenea planorbis, according to Jeffreys, " occasionally sus- 

 pends itself in the water by spinning a viscous thread with its 

 foot."§ 



JeFFREYSIIDjE. 



Jeffreysia diaphana, also, according to the same author, 

 " spins a slimy suspensile thread." || 



Litiopid^. 



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). Belanger 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 



* Jeffreys, torn, cit., p. 57. 



f Lindstrom, ' Om Gotlands nutida mollusker,' 1868, p. 26. 



| Tye, 1874, I. c. ; 1878, I. c. 



§ Jeffreys, torn, cit., p. 66. || Jeffreys, torn, cit., p. 60. 



