124 University of Calif ornia Publications in Zoology. [Vol. 8 



utes after sunset the number of specimens increased 409 times, and during 

 the next 3 hours it decreased, which suggests that the species attains its 

 maximum abundance within an hour after sunset. 



7. On February 8, 1910, the sun set at 5:50 p.m. Three surface hauls 

 (2010, 2014, and 2024) were made. The first, lasting from 2:52 to 4:25 

 p.m., contained 55, the second, lasting from 4:50 to 6:15 p.m., contained 

 220, and the third, lasting from 6:57 to 7:54 p.m., contained 165 specimens. 

 Expressed according to hour-hauls these numbers are 35, 155, and 174. This 

 means that from 3 hours before till 25 minutes after sunset the number 

 increased fourfold, while it increased but slightly during the next hour and 

 49 minutes. 



8. On March 17, 1910, the sun set at 6:10 p.m. Six surface hauls (2070, 

 2078, 2082, 2085, 2096, and 2101) were made. They lasted respectively from 

 1:30 to 2:18 p.m., 2:20 to 3:34 p.m., 3:40 to 4:30 p.m., 4:45 to 5:10 p.m., 

 6:15 to 6:50 p.m., and 6:55 to 7:30 p.m. They contained respectively 3, 4, 

 13, 7, 125, and 472 specimens. Expressed according to hour-hauls these 

 numbers are 4, 3, 16, 17, 214, and 809. Hence, during the period of 4 hours 

 before sunset the number of specimens only quadrupled, while an hour after 

 sunset found the number 13 times larger, and during the succeeding 40 

 minutes the number quadrupled again. 



The following instances (9 to 13) concern variation in 

 abundance relative to sunrise. 



9. On June 27, 1908, sunrise occurred at 4:53 a.m. Two surface hauls 

 (1509 and 15r2) were made which lasted respectively from 5:58 to 6:15 a.m. 

 and 6:20 to 6:45 a.m. The former contained 72 and the latter 60 sjiecimens 

 of S. bipunctata. Expressed according to hour-hauls these numbers are 306 

 and 120, which means that the number of specimens on the surface 1 hour 

 and 52 minutes after sunrise was appro rimat el y one-third of that present 

 30 minutes earlier. In this instance the first haul began an hour after sun- 

 rise, so it is probable that the morning maximum occurred before the time 

 of hauling. 



10. On July 24, 1908, the sun rose at 5:08 a.m. Two surface hauls (1597 

 and 1600) lasted respectively from 4:26 to 4:46 a.m. and 4:58 to 5:18 a.m. 

 The former contained 75 and the latter 3 specimens of S. bipunctata. Ex- 

 pressed accordng to hour-hauls the numbers are 229 and 9. This means that 

 22 minutes before sunrise the animals tvere 25 times more abundant than at 

 10 minutes after sunrise. 



11. On July 2, 1909, the sun rose at 4:55 a.m. Haul 1784 lasting from 

 4:50 to 5:11 a.m. contained 618, and haul 1791 lasting from 6:37 to 7:00 

 a.m. contained 41 specimens of S. bipunctata. Expressed according to hour- 

 hauls the numbers are 1769 and 104. In other words, the number of speci- 

 mens on the surface 16 minutes after sunrise was 17 times greater than that 

 1 hour and 40 minutes later. 



12. On July 9, 1909, the sun rose at 4:59 a.m. Three surface hauls 

 (1850, 1854, and 1860) lasting respectively from 3:30 to 4:13 a.m., 4:20 to 

 5:15 a.m., and 5:18 to 6:25 a.m. were made. The first contained 270, the 



