70 THE SCALLOP FISHERY 



drill {TJrosalpinx cinerea) (Kg. 68) is generally present. This little 

 gasteropod moUusk, next to the starfish, is the most destructive enemy 

 of the scallop and oyster, and is found in nearly every scalloping lo- 

 cality. Scarcely more than an inch in height and of an innocent grey 

 color it has proved a source of trouble to the oysterman, owing to the 

 impossibility of thoroughly removing it from the oyster beds. 



Its method of attack is to crawl upon the upper valve of the scallop 

 and then pierce a hole in the thin shell, scarcely larger in diameter 

 than a needle, by means of a tiny ribbon-like tongue armed with fine 

 teeth. When the boring is completed the animal sucks out the contents 

 of the shell. Scallops have been found destroyed by the drill bearing 

 on the shell a row of globular egg cases which the drill had deposited. 

 It is during this process that the scallop has an advantage over the 

 oyster. The latter is fixed and immovable, the former is capable of 

 movement, and by a few well-directed flaps of the shell can in many 

 instances throw off the intruder and escape destruction. The numerous 

 half punctures in many living scallops bear witness to the inability of 

 the " borer " to finish its task. 



A few observations upon the length of time it takes to bore and eat 

 a scallop were made at Monomoy Point with a view of determining the 

 actual extent of destruction. Scallops were confined with the drills 

 in boxes with netting tops. Different numbers of scallops and drills 

 were used for over a month. As many as five drills have been found 

 on one scallop not in confinement, and as many as two or three are of 

 common occurrence (Fig. 95). The conclusion arrived at from these 

 observations was that it took from four to six days for the drill to 

 pierce the shell sufflciently to eat the contents, and that the meal was 

 consumed in about the same amount of time. At this rate the drill 

 could only eat about three large scallops per month, even if nothing 

 interfered with the operation, and in the long run the amount of 

 destruction would be extremely slight. While the unnatural condition 

 of the confined animals may have made the process slow, the limited 

 area afforded the scallop but slight chance to escape from its enemy 

 and so partially offsets any error. 



(c) Nassa obsoleta The third active enemy of the scallop is per- 

 haps hardly to be classed under that head. It is the scavenger of the 

 tidal flats, the little black winkel, Nassa obsoleta, which has the im- 

 portant duty of cleaning the flats. The actual damage done by this 

 animal is comparatively small, as it is not an inhabitant of the same 

 localities as the scallop as a rule, being found between the tide lines. 

 Nassa is commonly thought to be of little damage to living shellfish, 

 though it is known to eagerly devour any dead or broken specimens. 

 Although the damage is of little account the method of attack is so 

 interesting that it will bear relating. The scallop when resting on the 

 bottom with tentacles extended is at times extremely sensitive, and then 



