SPINNING MOLLUSCS. 317 



a Cerithidea ; general statements occur in the books also for 

 Cerithium and Potamides, but these rise out of synonymy, the 

 animals referred to being respectively Bittium and Cerithidea. 

 Our little Bittium reticulatum* according to Jeffreys, " crawls 

 actively and quickly by means of its long foot, and occasionally 

 suspends itself by a byssal filament to a bit of floating seaweed, 

 or to the side of the vessel in which it is kept."t Cerithiopsis 

 tubercularis, another little mollusc of our coasts (shell generally 

 about £ in. long), resembles the Bittium in its active crawling 

 habits. " When at rest," according to Jeffreys, " it spins a fine 

 transparent thread, which issues from the opening in the centre 

 of the foot-sole, its end being attached by the point of the foot 

 to some foreign substance." The author, on one occasion, drew 

 the shell up by the thread with a camel's-hair brush, and kept 

 the creature thus suspended in the water for several seconds, the 

 foot being doubled up.+ Cerithidea obtusa,§ which is a mollusc 

 of good size, presents one of the most curious of the cases 

 noticed in this paper. It lives in brackish water, in mangrove- 

 swamps, and the mouths of rivers in Singapore and Borneo ; 

 sometimes it crawls on stones and leaves in the neighbourhood, 

 and, according to the observations of A. Adams, it is not un- 

 frequently found suspended by glutinous threads to boughs and 

 the roots of the mangroves, as represented in fig. 6. Further, 

 according to the same observer, " when the animal hybernates, 

 it retracts itself into the shell, and brings its operculum to fit 

 closely into the aperture, after having previously affixed sixty or 

 seventy glassy, transparent, glutinous threads to the place of 

 attachment, when they occupy the outer or right lip and extend 

 half-way round the operculum." || Von Martens has observed 

 that the attachment of this mollusc and of " Megalomastoma 

 suspensum " (fig. 4) make a remarkable approach to the attach- 

 ment of bivalves by a byssus,H but this remark, the writer pre- 



* Cerithium reticulatum. 



f Jeffreys, torn. cit. p. 260. J Ibid. p. 268. 



§ Cerithium truncatum, C. obtusum. 



|| A. Adams, « Zoology of the Voyage of H.M.S. Samarang : Mollusca,' 

 1848, pp. 43-4; and see also 'Narrative of the Voyage,' ii. (1848), pp. 389, 

 509 ; ' Proceedings of the Zoological Society of London,' 1847, pp. 21-2 ; 

 and 'Annals and Magazine of Natural History,' xix. (1847), pp. 413-4. 



IT E. v. Martens, ' Zoologischer Anzeiger,' i. (1878), p. 251. 



