230 U. S. BUREAU OF FISHERIES 



The survey of the distribution of the oj^ster drill in Hampton 

 Eoads showed that it is limited to localities having salinities higher 

 than 12. It was observed that it was more numerous on cultivated 

 beds than on natural beds. The animal never is found on muddy 

 bottoms, but inhabits hard bottoms {'' natural " rocks and planted 

 grounds) at depths between 5 and 25 feet. 



The depredations caused by the oyster drill are not as great as has 

 been claimed, the percentage of deaths due to " drills " rarely exceed- 

 ing 20 per cent. Usually it lies between 3 and 8 per cent. 



The animals remain inactive in winter and do not feed. They 

 begin to feed and spawn when the temperature of the water reaches 

 approximately 70° F. (about May 15 to 20). Spawning occurred 

 from May 20 to September 15 in 1927, being most intense during 

 June and July. Each female was observed to spawn but once. The 

 average number of egg cases laid by a single female is 25 and the 

 average number of eggs in a case is 8. Thus, each female lays about 

 200 eggs. About half of these hatch in 35 to 40 days. The drill 

 stops spawning as soon as the temperature drops below 70° F. It 

 feeds almost continuously during the summer. The rate of "drill- 

 ing" into oyster shells is 0.40 millimeters per day. Although the 

 perforation may be made anywhere on either valve, examination dis- 

 closes that 74 per cent of the holes occur on or near the place of 

 muscle attachment. Besides oysters, the oyster drill has been ob- 

 served feeding on small crabs, barnacles, clams, mussels, and Crep- 

 idula. 



Studies on the behavior of Urosalpimc cinerea give the following 

 results : 



1. The animal is negatively geotropic. When placed in a dish, 

 the drill will creep upward until it reaches the surface of the water. 

 This reaction undoubtedly is effective to keep mud from the mantle 

 chamber. It is important in spawning, also. It was observed that 

 the eggs always were laid on some object off the bottom. This would 

 prevent their suffocation by the mud. 



2. The oyster drill is rheotropic. When placed in a current, the 

 animal will orient so as to point its siphon upstream and then move 

 against the current. This behavior may be of importance in the 

 distribution of the animal, but it seems probable that in a region like 

 Hampton Roads, where the currents are tidal, it can not have great 

 effect. 



In studying the migration of the drill, 577 tagged animals were 

 released in different localities and on various bottoms. Only those 

 placed on oyster beds yielded information. Of these, 28 were re- 

 covered. They showed that the oyster drill migrates very little, the 

 greatest distance traveled being 200 feet in one month. 



SCALLOPS 



Scallop investigations in North Carolina, begun in July, 1925, by 

 J. S. Gutsell at the request of the Fisheries Commission Board of 

 North Carolina, were continued in 1927. Spawning, growth, lon- 

 gevity, and distribution were studied. It was found that in 1927 

 spawning continued through January, and that probably it began 

 early in August or even July in 1926. Very young scallops occur in 



