Page:The Zoologist, 4th series, vol 4 (1900).djvu/347

Rh 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." Cerithiopsis tubercularis, another little mollusc of our coasts (shell generally about ¼ 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 unfrequently 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 attachment of bivalves by a byssus, but this remark, the writer pre-