1912] Esterly: Copepoda of the San Diego Region 315 
Pleuromamma gracilis —This species was taken in seven sur- 
face hauls, all of which were at night and took 213 animals. The 
largest number of animals was 165 between 8 and 10 p.m. The 
horizontal closing nets took P. gracilis but once, a haul between 
6 and 8 p.m. at 7.5 fathoms containing one animal. Six hauls 
with the vertical closing nets obtained 316 animals. One of 
these (no. 2053) contained 253 specimens; this haul was from 
200 to 150 fathoms in the middle of the afternoon. None of 
the animals was taken above 150 fathoms with the closing nets 
except at night, and the center of migration may be taken as 
150 fathoms. 
The lowest and highest surface temperatures at which P. 
gracilis was taken are 13°8 and 20°2 respectively; the salinities 
range from 33.578 to 33.603. 
This species was taken in only one haul with the horizontal 
closing net. The results of collections with the vertical nets 
are shown in table 42. The center of migration is at 100-200 
fathoms (line 3), but there is little evidence of an upward 
migration except in the fact that that region is deserted at night. 
TABLE 42 
Distribution of Plewromamma gracilis as shown by hauls with the 
vertical closing nets, day and night hauls compared 
B Cc D E 
Total Successful Total Animals per Haul 
Depth hauls hauls animals 100-f. haul frequency 
Day Night Day Night Day Night Day Night Day Night 
ie 40-0 106 100 0 0 0 0 0 0 0 0 
2. 100-40 39 34 0 al 0 1 0 1 0 3 
200-100 12 uf 4 0 303 0 303 0 33 0 
250-200 6 1 1 0 2 0 4 0 16 0 
5. 300-250 4 1 0 0 0 0 0 0 0 0 
Pleuromanma quadrungulata—tThis is a very rare form at 
the surface, for it was obtained in only two day hauls which 
contained three animals. 
The closing nets obtained the animals in much larger num- 
bers, and both sorts of nets agree in that the day plurimum is 
at 200-250 fathoms. The results of- hauling with the horizontal 
closing nets are shown in table 43. The region of the day 
