308 THE ZOOLOGIST. 



tenacious thread of mucus." * It would have been interesting 

 to have had more particulars of this attachment, for, according 

 to Dr. Gibbons, the South African Cyclostomas fix their shells 

 by a brittle pellicle of dried mucus, proceeding from the edge of 

 the columellar lip, a mode of attachment, as he states, wholly 

 different from that of Chondropoma and Tudora, whose flexible 

 silk-like thread, as just mentioned, passes between the outer lip 

 and the operculum.! 



Littorinid^e. 



Gray has listed Littorina with Pectinibranchs capable of 

 making threads,! but the writer does not know on what authority. 

 For repose, out of the water, most of these Periwinkles closely 

 fix their shell by a pellicle of dry mucus, compared by Gibbons 

 to that of the Old-World Cyclostomas, and by Jeffreys and others 

 to the attaching film of Helix. $ Of Lacuna, however, which 

 belongs to this family, Jeffreys states that the creatures " occa- 

 sionally secrete slimy threads (like the Limax arborum), by 

 which they suspend themselves from the frond or stalk of a 

 seaweed."|| 



RissomE. 



The use of threads is presumably general among Rissoida — 

 small, often minute molluscs, which swarm on seaweeds and 

 grasswrack in pools and shallows, as well as on and under stones 

 in some of the deeper waters of the coast. It was in 1833 that 

 Gray made an often quoted observation to the Zoological Society 

 of London, that " the animal of Rissoa parva has the power of 

 emitting a glutinous thread, by which it attaches itself to floating 



* Woodward, * Proceedings of the Zoological Society of London,' 1859, 

 p. 204; and 'Annals and Magazine of Natural History' (3), iv. (1859), 

 p. 320. 



f Gibbons, 1878, torn. cit. p. 339 ; 1879, I. c. 



| Gray, 'Annals and Magazine of Natural History' (2), ix. (1852), 

 p. 216. 



§ Gibbons, 1878, I. c. ; 1879, I. c. ; Jeffreys, ' British Conchology,' iii. (1865), 

 p. 363 ; Bouchard-Chantereaux, ' Memoires et Notices de la Societe d'Agri- 

 culture, du Commerce et des Arts, de Boulogne -sur-Mer, 1835, pp. 155-7 ; 

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

 A. d'Orbigny, ' Histoire Naturelle des lies Canaries : Mollusques,' 1839, 

 p. 79. 



|| Jeffreys, torn. cit. p. 343. 



