SPINNING MOLLUSCS. 309 



seaweeds, and is enabled, when displaced, to recover its previous 

 position";* and we find it is stated by Jeffreys, for Rissoa gene- 

 rally, that the foot is grooved down the middle for about half its 

 length towards the tail, whence it emits a glutinous thread, by, 

 which the animal suspends itself to foreign bodies or to the sur- 

 face of the water.! " Lying on a rock by the brink of a seaweed- 

 covered pool left by the receding tide," says Jeffreys, writing of 

 Rissoa parva, " it is no less pleasant than curious to watch the 

 active little creature go through its different exercises — creeping, 

 floating, and spinning."]: By " floating " the author means, evi- 

 dently, creeping at the surface of the water, a habit which here, 

 as in other molluscs, seems intimately associated with that of 

 " spinning." The same naturalist mentions the latter habit in 

 several other species : Rissoa membranacea, he says, " occasion- 

 ally floats, or suspends itself by a viscous thread " ; jR. vitrea 

 " suspends itself by a single byssal thread, keeping the mouth of 

 the shell closed by the operculum"; R. abyssicola "floats like 

 its congeners, and suspends itself in the water by a single byssal 

 thread " ; R. pulcherrima, exceedingly agile both in creeping and 

 floating, " spins a delicate thread of attachment " ; and the very 

 tiny R.fulgida was frequently observed by the author " spinning 

 a fine transparent slimy thread, and thus hanging suspended to 

 a bit of seaweed or to the surface of the water." R. cancellata, 

 Jeffreys further says, " is active and bold, floats like its congeners, 

 and spins a byssal thread instantly on being detached from a 

 crawling position " ; R. carinata,§ moreover, like R. cancellata, 

 " adheres with some tenacity to the stones on which it is found, 

 and, when detached, it also spins a fine byssal thread, by means 

 of which it suspends itself in the water."|| This last species.1T 

 according to Mr. Brockton Tomlin's experience in the Channel 

 Islands, is usually found under rather deeply-buried stones, to which 

 it moors itself, he says, by a strong " byssus";** each individual, 

 this observer obligingly tells the writer, had more than one short 

 thread, generally, as far as he remembers, four or five. Barleeia 

 rubra, according to Jeffreys, creeps at the surface, foot uppermost, 



* Gray, ' Proceedings of the Zoological Society of London,' 1833, p. 116. 

 f Jeffreys, op. cit., iv. (1867), p. 1. { Jeffreys, torn, cit., pp. 25, 26. 



§ B. striatula.. || Jeffreys, torn, cit., pp. 6, 10, 20, 32, 41, 43, 44. 



IT E. striatula. ** Tomlin, 'British Naturalist,' iii. (1893), p. 123. 



