90 
BULLETIN OF THE BUREAU OF FISHERIES 
During the summer of 1927 preliminary experiments to determine the lower 
lethal salinity were made at Norfolk, Va., on snails collected from Hampton Roads. 
The animals used were taken from two localities, the June salinities of which averaged, 
respectively, 15 and 20 parts per mille. They were kept in the laboratory for about 
six weeks where the salinity was taken daily and where it never rose over 20 parts 
per mille. The two sets of drills were mixed and specimens for experimentation 
taken at random. 
The procedure was as follows: Salinities between 5 and 17 parts per mille at 
intervals of approximately 2 parts per mille, obtained by diluting sea water with 
distilled water were used. The animals, 20 at each salinity, were immersed in the 
water and kept submerged by means of a wire screen stretched below the surface. 
The jars (of approximately 2 liters capacity) were kept loosely covered to prevent 
excessive evaporation, and the water was oxygenated twice daily by vigorous stirring. 
That this was sufficient is shown by the fact that drills will live in jars of sea water 
for several months without change of water or oxygenation. Temperature, salinity, 
and pH were taken daily and the condition of the animal noted. The criterion of 
death was whether or not the mantle would respond to a needle prick. When an 
animal was found that did not respond to this stimulus it was removed from the 
experimental jar and placed in running sea water to determine whether or not it 
would recover. In every case the animal would by putrefying within a few days 
give conclusive evidence that water of that salinity was lethal to the specimen. 
Death was always preceded by the animal becoming unattached, and at the lower 
salinities the animal swelled and protruded from the shell before dying, owing 
undoubtedly to the difference in osmotic pressure. The animals were kept under 
observation for 10 days, at the end of which time the surviving drills were returned 
to running sea water and their activity noted. Three different sets of observations 
comprise these experiments. (Table 2.) 
Table 2. — Effects of varying salinity on Urosalpinx cinerea, from Hampton Roads, summer of 1927 
Items 
Experiments 
No. 1 
No. 2 
No. 3 
Salinity at which drills were killed 
10.12 
90 
12.26 
95 
10 
26 
12.52 
75 
15.05 
90 
5 
8- 8.2 
11.35 
90 
13.91 
85 
15 
24 
7.9- 8.2 
Percentage of deaths after 10 days __ 
Salinity at which drills survived 
Percentage of survival after 10 days 
Percentage of deaths in control- __ _ 
Average temperature for period (°C.) 
pH for period 
During the summer of 1928 experiments, similar to those mentioned above, 
were made on drills collected at Beaufort, N. C., where the summer water salinity 
rose as high as 37 parts per mille and remained well over 30 for the entire season. 
The following modifications were made in the procedure as given for the Norfolk 
experiments: (1) The water was oxygenated by bubbling a continuous stream of 
air through it; (2) instead of using the mantle as a criterion of death, the tip of the 
siphon was employed for this purpose. The results, which are preliminary, are given 
in Table 3. The pH values, which are rather high, remained with but small vari- 
ations between 8.4 and 8.8. The continuous stream of air through the sea water 
brought about a small increase in the pH during the first 24 hours, after which it 
