44 ZOOLOGY OF THE VOYAGE OF H.M.S. SAMARANG. 



The animal of Ceritldum obtusum lias a broad; suborbicular, and expanded foot, and an 

 elongated, snbcylindrical, annulated trunk, of a light brown colour, with three rather broad, 

 well-defined, opake, yellow lines extending along its upper surface, the central one of which 

 extends from the head to very near the extremity of the proboscis, where it is bifid, the two 

 forks diverging ; the two lateral lines are shorter, not bifid at their extremities, and reach 

 forward on the head to within a little distance of the origin of the tentacles ; the tentacles 

 are very short, annulated, with the eyes (which are small, though with a distinct iris and 

 pupil) situated at their tip, whereas they are mostly placed on tubercles situated on the outer 

 side of the base of the tentacles, or on the tentacles themselves at a little distance from their 

 origin. The foot is of a light pinky brown on its upper surface, mottled with a deep, rich 

 brown, and on the under surface is lilac. 



The Cerithia obtusa live in brackish water in mangrove-swamps and the mouths of 

 rivers, in Singapore and Borneo. Sometimes they crawl on the stones and leaves in the 

 neighbourhood, and are not unfrequently found suspended by glutinous threads to boughs 

 and the roots of the mangroves, as represented in our plate. The operculum is round, horny, 

 with a central nucleus and concentric elements ; it is semitransparent, and borne upon the 

 posterior part of the foot at its extreme end. 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. 



A species of Cychstoma {Megalomastoma stispensicm, Guilding) was found by the 

 Rev. Lansdowne Guilding at the Island of St. Vincent, suspended in like manner from the 

 trees ; and Bissoa parva has been observed by Mr. Gray, upon our own shores (Pro. Zool. 

 Soc. 1833, p. 116), to have the power of emitting a glutinous thread by which it attaches 

 itself to floating sea-weeds. 



There is a very handsome Cerithium closely allied to the foregoing, which I have frequently found 

 crawling languidly on the leaves of the Pontedera and sedges in the tluviatile marshes on the banks of the 

 rivers in many parts of Borneo, and many miles in the interior where the water is perfectly fresh, and 

 which has the eyes likewise terminal and the proboscis marked with crimson and yellow ; the foot is very 

 dark brown, and has a vivid scarlet line extending round the lower margin. The position of the eye 

 varies considerably in this group. In an amphibious Bornean species, allied to C. decollatum, they are 

 terminal at the end of peduncles ; in other words, the tentacles are connate with the eye-peduncles for 

 the whole of their extent. In C. mieroptera the tentacles extend a third beyond the eye-peduncles ; in 

 C. decollatum the eye-peduncles are truncated, with the eyes at the end, while the tentacle extends beyond 

 them in the form of a minute filament ; all these species have circular multispiral opercula. 



In another species, from the Island of Billitou, coral reef, two fathoms and a half, the animal is of a 

 greenish brown, minutely punctulated with darker brown, and covered moreover with small, light red, 

 round spots. The operculum is oval, horny, and semipellucid, the elements not concentric, curving 

 from a nucleus at the anterior extremity towards the periphery. In this species the foot is moderately 



