110 
BULLETIN OE THE BUREAU OP FISHERIES 
SUMMARY 
The preceding studies may be summarized as follows : 
1. The common oyster drill ( Urosalpinx cinerea) is a carnivorous gastropod, about 
three-quarters of an inch in length, possessing a hard calcareous shell varying in color 
from light brown to white. The animal is small, the foot scarcely covering the aperture. 
2. The snail inhabits the marine and brackish waters of the Atlantic coast from 
Maine to Florida, occurring also in San Francisco Bay, Bermuda, and England. At 
Hampton Roads it is found only below the low-water mark while in Connecticut and 
North Carolina it is present on beds exposed at low water. Muddy bottoms, clear 
sands, and depths greater than 25 feet are unfavorable for its growth and multiplica- 
tion. More animals occur on planted bottoms than on natural rock. 
3. Laboratory experiments at Hampton Roads and at Beaufort on the salinity 
death point of the drill, collected from areas having different average salinities, show 
that the salinity at which the animal dies (or the salinity limiting the distribution of 
the animal) depends upon the salinity of the environment from which the animal has 
been collected. In other words, the snail is capable of a large degree of adaptation 
to low salinities. It is important to know just how far this adaptation can be carried 
in order to know whether or not the setting areas will ever be threatened. 
4. The exact mechanism of creeping in the oyster drill is still unknown. Either 
it creeps by muscular activity (arhythmic pedal waves) or through the cilia of the 
pedal surface. Tagging experiments, distribution observations, and an analysis of 
the older literature show that the animal does not migrate but that its distribution is 
dependent on the planting activities of man and on the migrations of other animals 
such as crabs to which they sometimes attach themselves. 
5. Observations on the relation between temperature and the activities of the 
animal show that: (a) The animal becomes inactive at temperatures below 10° C.; 
(6) feeding does not occur until the surrounding temperature reaches 15° C.; and (c) 
spawning takes place only when the temperature is above 20° C. 
6. Hampton Roads has not suffered as greatly from this predatory gastropod as 
has been reported. The percentage of deaths from drills in relation to the number of 
live oysters present rarely exceeds 3 per cent excepting on planted beds where it is 
sometimes as high as 20. Areas, where setting occurs and where beds of young oysters 
are found, necessarily suffer greater damage because the spat are more easily pierced 
and yield only a small amount of food. The mechanism of drilling is the radula, a 
rasplike organ which moves over its cartilages much as a belt over a pulley. Urosalpinx 
confines itself not only to drilling a great many living mollusks and crustaceans, but 
will also feed on the meats of these animals. Although out of a batch of oysters of 
all sizes the smallest and thinnest shelled are killed first, it has been shown that all 
oysters, no matter how large, are attacked by the drill. The choice of the valve 
drilled depends on many factors which are enumerated and the significance of each 
given in the text. The place of perforation depends on factors not yet known. In 
three-quarters of the valves examined, the hole occurred at or near the place of muscle 
attachment although any portion of the shell may be drilled. In oysters, drilling 
progresses at approximately 0.4 millimeter per 24 hours. The behavior of the oyster, 
after being drilled, depends largely upon the position of the hole. It is believed that 
the drill injects some fatal toxic substance into the body of the oyster. 
7. Although there is no sexual shell characteristic in Urosalpinx cinerea, the 
sexes are separate. The eggs are laid in leathery, vaselike capsules attached to the 
