UNIVALVE MOLLUSCS 379 



at the same rate as the coral. As the original shell and the lower portion of the 

 tube become buried in the coral they are rilled up with solid shelly material, the 

 soft parts of the mollusc being contained in a cavity at the top of the tube. 



Of a more normal type are the dog-whelks, the shells of one of which, Nassa 

 callosa, when cut into transverse sections form the dewarra-money of New Britain 

 that passes current at three shillings a fathom. To another family belongs 

 Turbinella rapa, the famous chank-shell carried by the images of Vishnu, the 

 Hindu deity, of which the left-handed variety is held sacred. This shell comes 

 chiefly from Tuticorin, in the Gulf of Manar, where the licences paid by the divers 

 used to bring in a revenue of £4000 a year to the Government of Ceylon. To the 

 allied family, Buccinidce, of which the common whelk (Buccinuvi undatum) 

 and the red whelk (Fusus antiquus) are well-known British representatives, 

 belongs the unicorn-shell (Latirus cingulatus), characterised by the presence of a 

 long tooth -like process on the centre lip of the shell. It is a general belief that 

 whelks (under which term may be included a number of genera of solid-shelled 

 molluscs belonging to the families Buccinidce, Nassidce, and Muricidce) obtain 

 access to the interior of the oysters, mussels, and other bivalves which form their 

 food by boring through the shell with their ' chain-saw ' tooth-ribbon, and then 

 sucking out the flesh by means of their long proboscis. Such a method of attack 

 has been observed in the case of the little purple-yielding whelk (Purpura), of our 

 own shores, but is apparently not followed by the dog-whelk (Nassa), which has 

 been seen to wedge its own shell between the gaping valves of the clam or 

 mussel selected as a victim. This latter method of attack is also the one employed 

 by the large American whelks of the genus Fulgur and its sub-genus Sycotypus. 

 Some of these whelks were kept in a salt-water tank, where they were fed on live 

 oysters, clams, mussels, etc. In the case of oysters the whelk crawled on the top 

 of the bivalve, which closed its valves, only to reopen them after the lapse of a few 

 minutes. Thereupon the attacker inserted part of its own shell in the gap, and 

 immediately after introduced its proboscis. Fifty minutes later it left the empty 

 shell ; while after the lapse of another twenty minutes it set about serving a 

 second oyster in the same way. These whelks will eat a couple of oysters one day 

 and as many the next, but after this they fast, and lie buried in the sand. In the 

 case of clams or gapers (My a) no insertion of the shell of the whelk is necessary, as 

 the valves have an aperture, even when closed, into which the proboscis can be 

 inserted. Bivalves of the genus Venus are attacked in a different manner; the 

 whelk grasping the bivalve in the hollow of its muscular foot, and then bringing the 

 edges of the valves of the former against the margin of its own shell. By contract- 

 ing its muscles it forces the margins of the valves together, which results in a small 

 fragment being chipped from one of the shells of the Venus. This is repeated till 

 the crack becomes wide enough for the proboscis of the whelk to be brought into 

 play. The insertion may take place either through the flattening out of the 

 proboscis, by the introduction of a secretion which causes the Venus to gape, or by 

 the insertion of the shell of the whelk between the valves. The Venus is more 

 sensitive to external stimulants than is the oyster, and when once in the grasp of 

 its deadly enemy never opens its valves voluntarily. An oyster, on the other 

 hand, after recovering from the first shock, opens its valves wide, altogether 



