STUDIES or THE OYSTER DRILL 
89 
Table 1 . — The relation between the number of drills and various environmental factors 
[Survey made at Hampton Roads during June, 1927. See fig. 2] 
Station 
Drills present 
in a unit area 
Salinity 
in parts 
per mille 
pH 
Depth 
in feet 
Character 
of bed 
Station 
Drills present 
in a unit area 
Salinity 
in parts 
per mille 
pH 
Depth 
in feet 
Character 
of bed 
Alive 
Dead 
Alive 
Dead 
Number 
Number 
Number 
Number 
A 
1 
17. 00 
7.8 
12 
Natural. 
S 
3 
2 
18. 00 
7.8 
10 
Natural. 
B 
3 
17.00 
7.8 
Do. 
T 
2 
17. 25 
8.0 
4 
Planted. 
D 
1 
18. 00 
7.9 
7 
Do. 
u 
13 
3 
20. 00 
8.4 
14 
Do. 
E 
8 
4 
15. 00 
8.0 
10 
Do. 
W 
18 
2 
17. 00 
8.2 
9 
Do. 
F 
g 
15. 50 
12 
Do. 
X 
13 
17.00 
8.0 
Do. 
G 
11. 50 
8.0 
5 
Do. 
z 
5 
17. 25 
8.3 
12 
Do. 
H 
11. 50 
8.0 
5 
Do. 
AA 
3 
4 
19. 50 
8.3 
7 
Do. 
13. 00 
8.0 
2 
Do. 
BB 
5 
19. 30 
8.2 
6 
Do. 
K 
16. 50 
8.0 
5 
Planted. 
16 
17 
5 
17. 00 
8.2 
10 
Do. 
L 
2 
17. 00 
8.0 
Do. 
18 
14 
2 
17. 25 
8.0 
9 
Do. 
0 
3 
17. 00 
8.0 
g 
Do. 
19 
16 
4 
17. 25 
11 
Do. 
p 
2 
l 
17.50 
7.8 
12 
Natural. 
27 
4 
2 
15. 25 
7.9 
12 
Natural. 
Q 
16 
2 
19. 25 
8.2 
15 
Planted. 
45 
17 
17. 00 
7.8 
10 
Planted. 
R 
2 
1 
17. 00 
7.9 
m 
Natural. 
The drill is found over the whole area of Hampton Roads, being more abundant 
on the planted areas than on the natural rock, a condition that is explained by the 
absence of any migratory habits. Salinity below 15 parts per mille, muddy bottoms, 
clear sands, and depths greater than 25 feet are factors unfavorable for its growth 
and multiplication. At Beaufort it flourishes and reproduces at average summer 
salinities of 35 parts per mille. In Hampton Roads the snail does not occur above 
the low-water mark, but in Connecticut and in North Carolina it is found on beds 
exposed at low water. 
SALINITY AND DISTRIBUTION 
Although many investigators have studied the adaptation of organisms to vary- 
ing salinities, the mechanism for this adaptation, the relation between the environ- 
mental salinity and the salt content of the blood, the importance of salinity as a 
barrier to the multiplication and distribution of a species, and the lethal salinities 
for several animals (see Duval, 1925, for complete bibliography); no attempt, so far 
as the author knows, has been made to correlate the death-point salinity with the 
salinity of the environmental waters. During these studies certain data were col- 
lected on the resistance of Urosalpinx to low salinities. Three sets of data are avail- 
able, one gives the results of a preliminary experiment made at Norfolk during the 
summer of 1927; the other two sets of data were collected at Beaufort, N. C. The 
latter are more complete and permit of more accurate analysis. The conclusions 
from these observations, already published elsewhere (Federighi, 1931), are given 
in the following paragraphs. 
Moore (1911) stated that in Delaware Bay the oyster drill does not thrive at 
specific gravities below 1.012 to 1.013 (salinity: 15.50-17 parts per mille). In 1923 
Nelson gave the minimum salinity for the survival and reproduction of this gastropod 
in New Jersey as 18.33 parts per mille — a figure that has recently (1928) been lowered 
to 15 parts per mille (private communication). At Hampton Roads, according to 
the author’s observation made in June, 1927, the snail does not normally inhabit 
waters of salinities below 15 parts per mille. What the upper salinity limit may be 
is shown by observations made at Beaufort, N. C., where drills were found living 
and reproducing in areas where the summer salinities run as high as 37 parts per 
mille for several days (summer, 1928). 
