98 
BULLETIN OF THE BUREAU OF FISHERIES 
were made over the various oyster beds at Hampton Roads. Oysters were dredged 
from the desired area, culled, and the dead shells picked out. A record was kept of 
the total number of live oysters, the total number of dead shells, and tne number of 
“drilled” shells. From these figures the percentage of damage was determined. 
The surprising fact was the unexpectedly small percentage of deaths from the drill. 
Table 6 gives a summary of the percentages. 
Table 6. — Damage caused by Urosalpinx cinerea over Hampton Roads for June, 1927 
Station 
Live 
oysters 
Dead 
shells 
Drilled 
shells 
Dead 
oysters 
Oysters 
killed by 
drills in 
relation 
to live 
oysters 
Pig Point ■■ 
Number 
605 
Number 
104 
Number 
21 
; Per cent 
14.7 
Per cent 
13.5 
Craney Island Crook 
408 
75 
5 
15.5 
1.2 
Craney Island Flats 
103 
75 
42.0 
7.8 
Mouth of Nansemond River 2 _ 
no 
53 
32.5 
.9 
East Spit 2 
353 
103 
28 
22.5 
72 
1 
34.5 
l! 4 
Western branch of the Elizabeth River 2 
93 
32 
25. 5 
1.0 
709 
138 
32 
16.5 
14.5 
Little Bay 
332 
113 
42 
25.5 
i 12.7 
885 
290 
180 
25.0 
i 20.0 
Tanners Creek - - 
87 
31 
26.5 
■ Planted areas. 3 Stations Nos. 27, E, and E. 
2 Drills absent. 1 Stations Nos. 33 and 34. 
The significant figures are in column 6; that is, the percentage of drilled shells 
referred to the number of live oysters present. These figures show that the percentage 
of deaths due to the oyster drills is much higher on cultivated oyster grounds than on 
natural oyster rock, the average for planted bottoms being approximately 10 per cent, 
that for natural rock approximately 2 per cent. This difference is correlated with the 
greater number of oyster drills present on cultivated grounds. Why more drills are 
present on the cultivated areas undoubtedly seems to be explained by the following : 
(1) The distribution of the drill by man; and (2) the presence of practically unlimited 
amounts of food. 
Although several explanations — Stimpson, 1860 (from Colton, 1908); Ingersoll, 
1884 (from Colton, 1908); Schmienz, 1891 (from Flattely and Walton, 1922) ; Herrick, 
1906 ; and Colton, 1908 — as to how the carnivorous gastropods attack their victims have 
been advanced, the accepted mechanism by which food is obtained is the rasplike 
radula along with its cartilage and muscles, the whole organ being called the odonto- 
phore. The “filing”' is done by the radula, a ribbonlike rasp, on which the teeth are 
fixed. As this wears out it is replaced from the radula sac, growing forward like a 
nail over its bed as fast as it is worn out in front. The exact method by which the 
radula is moved has been studied by many investigators. Two theories have been 
brought forward: (1) The radula moves relatively to its cartilages and its rasping 
action is due to its own proper motion; (2) the radula remains at rest relatively to 
its cartilages, and its rasping action is due to the movements of its cartilages. The 
former was originally advanced by Huxley (1853) a view accepted by Wegmann 
(1884) and Oswald (1894), later corroborated by Herrick (1906), and at present the 
accepted one. The latter interpretation is that of Lacaze-Duthiers (1856) and Geddes 
(1879). Whether or not acid is secreted to aid the drilling is still a moot question, 
although glands capable of secreting acid have been described in some prosobranchs 
(Tryon, 1880). 
