2l6 BULLETIN OF THE BUREAU OF FISHERIES. 



appetites; specimens less than a quarter of an inch in diameter were observed strip- 

 ping the young mussels, little less than their own size, from wharf piles. Every star- 

 fish picked up was found in the act of eating a Mytilus. The larger starfish move 

 back and forth across the mussel beds in regular armies, up and down the wharf piles 

 and rocks where the mollusks grow, feeding on them at a rate which it is difficult to 

 estimate. 



The mussel, which heretofore has not been of sufficient commercial value to be 

 cultivated, has escaped the attention of the fisherman who would be the most capable 

 of estimating the depredations of its enemies. For the oyster, however, whose every 

 enemy is watched by the jealous cultivator, we have been able to learn more of the 

 devastating habits of the starfish. In Connecticut waters alone it was estimated in 

 1888 that this echinoderm destroyed $631,500 worth of oysters after not less than 42,000 

 bushels of the starfish had been removed from the beds. If mussels are a more favorite 

 food of the starfish, what must be the destruction wrought on the unprotected beds of 

 this shellfish ? The answer must be up in the hundreds of thousands of bushels. Mead 

 (1903) states that some mussel beds which had recently disappeared were probably 

 destroyed by starfish. Lebour (1907) states that a whole bed of mussels at the mouth 

 of the river Tyne, England, completely disappeared owing to the ravages of this animal. 



drills. 



The oyster drill, Urosalpinx cinerea, is a small snail commonly found on mussel 

 and oyster beds where it plays havoc with these bivalves, doing damage which undoubt- 

 edly amounts to thousands of dollars yearly. So great has been its injury to the oyster 

 beds that the United States Bureau of Fisheries has recently started a special investi- 

 gation to determine the possibility of protecting the oyster beds from its depredations. 

 T. E. B. Pope, who has been carrying on these investigations for the Bureau, finds 

 that the drills are abundant on the oyster beds where the salinity is above 1.010, and 

 that a single female is capable of producing about 100 young each season. Its method 

 of attack is like that of the winkles, Lunatia and Neverita. With a powerful radula it 

 is capable of drilling holes through shells of almost any thickness, but it prefers to prey 

 upon thin-shelled forms, such as mussels and young oysters. The time required to 

 perforate shells was found by Mr. Pope to be for oysters about \% inches long, two days; 

 2>2 inches long, 4 days; 3^ inches long, 6 days; 4 inches and over, 7 days. The per- 

 foration is made at no particular point on the shell, but is generally somewhere near 

 the middle of the valve. When completed the proboscis is thrust through the opening 

 to the soft parts on which the snail feeds. One drill was seen to kill five young oysters 

 in succession without taking any rest between its attacks. The author's experiments 

 with drills kept with mussels in a trough of running sea water demonstrated that the 

 time required for the snail to perforate the shell of a mussel less than an inch long was 

 about 18 hours, while for large ones the time varied from 24 to 36 hours. Figure 201 

 (opp. p. 216) shows a drill and a shell which was perforated by it. 



The dog-whelk, Purpura lapillus, is another species of drill similar in appearance 

 to Urosalpinx, but somewhat larger and more powerful. Its favorite food is the sea 

 mussel, which it attacks even more voraciously than does the oyster drill. It does not 

 cover such a wide area as the latter species, being confined to the rocky shallow waters ; 

 consequent!}- it is limited to doing much less harm than the oyster drill, which ranges over 



