48 THE NAUTILUS. 



had not been fed for a month or so ... . It attacked one of the 

 oysters five minutes after 1 placed them with it. . . . The Sycotypus 

 crawled on top of the oyster, which closed its valves. The conch 

 waited two minutes when the oyster opened its valves. Rotating 

 its shell on the axis of the columella through an angle of 70'^, it 

 thrust its own shell between the valves of the oyster and introduced 

 its proboscis between the shells. Forty minutes later it left the 

 empty shell. 



" Sycotypus does not wedge the shells of Mya apart, because it 

 can get at the soft parts without doing so, since the valves gap 

 slightly. To test this I introduced an oyster that had had three- 

 quarters of an inch broken from the margins of both valves on the 

 end away from the hinge so that the valves appeared to gap. I 

 found that Sycotopus attacked this one in the same manner as it 

 attacked 3Iya and did not wedge the shells apart. 



" Fulgur eating Venus is a much more complicated case. The 

 conch {Fulgur perversa or F. carica) grasps the Venus in the hollow 

 of its foot, bringing the margin of the Venus shell against its own 

 shell margin. By contracting the columellar muscle it forces the 

 margins of the shells together, which results in a small fragment 

 being chipped from the shell of Venus. This is repeated many times 

 and, finally, the crack between the valves is enlarged to a width of 

 3 mm. or more. The proboscis is normally about 5 mm. to 8 mm. 

 in diameter. There are three ways in which it may get at the 

 animal. First, it may flatten out its proboscis so that it will go 

 through the crack; secondly, it may pour in a secretion between the 

 valves which kills the clam, and, thirdly, it may wedge its shell 

 between the valves of the Venus. By contracting its columellar 

 muscle it may actually wedge the valves apart. Venus never opens 

 its valves of itself when it is in the grasp of a Fulgur, while Ostrea, 

 after the first shock, opens wide its valves as if no danger was near. 



'■'Fulgur and Sycotypus often break their own shell when opening 

 oysters and clams, and this accounts no doubt for the irregular 

 growth-lines seen on their shells. 



" This method of inserting the margin of a gasteropod between the 

 valves of a Lamellibranch has been noticed before. Francois (1890) 

 briefly reports that Murex fortispina has a special tooth on the mar- 

 gin of its aperture for the purpose of inserting between the valves of 

 Area. It may be that this manner of attacking the soft parts of 

 bivalves is a very common habit of Prosobranch mollusks." 



The several stages in the processes described are fully illustrated. 



NOTE. 



The scarcity of " copy " during the summer months has caused 

 us to issue a single number for August and September. The usual 

 number of pages for the year will be made up by enlarging a future 

 number. Plate IV. will appear next month. 



