1911] Michael: Cliaetognatha of the San Diego Region. 123 



from collections macie at consecutive times during the same day. 

 This will enable comparison of actual instead of average numbers 

 of specimens obtained. Because our closing nets were rarely 

 employed during consecutive times in the same depths, such 

 evidence relates entirely to surface collections. Here are a few 

 data. 



1. On JunQ 16, 1909, the sun set at 7:10 p.m. Four surface hauls (1650, 

 1653, 1655, and 1657) were made with the same net. The first lasted from 



.5:10 to 5:55 p.m., the second from 6:10 to 6:45 p.m., the third from 6:55 

 to 7:20 p.m., and the fourth from 7:25 to 8:00 p.m. The first haul con- 

 tained 15, the second 40, the third 75, and the fourth 5100 specimens of 

 S. bipunetata. Expressing these numbers with respect to hour-hauls, they 

 are 20, 69, 180, and 8743. In other words, from two hours before until 50 

 minutes after sunset the number of specimens on the surface increased 437 

 times and, while the number increased only 9 times during the first 2 hours 

 and 10 minutes, it increased 48 times during the next iO minutes. 



2. On the next day, June 17, 1909, sunset occurred between 7:10 and 

 7:11 p.m. From 5 to 6 p.m. one surface haul (1659) was made which con- 

 tained 13 specimens, and from 6:45 to 7:30 p.m. a second haul (1661) was 

 made which contained 550 specimens. Standardizing these numbers with 

 respect to hour-hauls, we find that S. bipunetata increased 56 times in abund- 

 ance from 1 hour and 10 minutes before till 20 minutes after sunset. 



3. On June 21, 1909, the sun set at 7:12 p.m. One surface haul (1673) 

 lasting from 6 to 6:25 p.m. contained 30, and a second haul (1680) lasting 

 from 7 to 7:35 p.m. contained 3600 specimens. In other words, the number 

 when standardized with respect to hour-hauls, increased 86 times from 47 

 minutes before till 23 minutes after sunset. 



4. On June 24, 1909, sunset occurred at 7:13 p.m. Haul 1728 lasting 

 from, 5:10 to 6:10 p.m. contained 72, haul 1731 lasting from 6:15 to 7:00 

 p.m. contained 50, and haul 1734 lasting from 7:03 to 7:40 p.m. contained 

 103 specimens of S. bipunetata. Expressing these numbers according to 

 hour-hauls they are 72, 67, and 167. Therefore, the number of specimens on 

 the surface increased threefold from 13 minutes before till 27 minutes after 

 sunset. 



5. On June 28, 1909, the sun set at 7:12 p.m. Haul 1744 lasting from 

 5 to 6:20 p.m. contained 2, haul 1751 lasting from 7:15 to 8 p.m. contained 

 155, and haul 1754 lasting from 8:10 to 8:50 p.m. contained 1100 specimens 

 of 8. bipunetata. Expressed according to hour-hauls these numbers are 2, 

 207, and 1650. Here the number on the surface increased 103 times from 

 52 minutes before till 18 mimites after sunset, ivhile during the next 50 

 minutes it increased only 8 times. 



6. On July 9, 1909, sunset occurred at 7:10 p.m. Haul 1868 lasting 

 from 7:03 to 7:36 p.m. contained 10, haul 1872 lasting from 7:40 to 8:15 

 p.m. contained 4300, and haul 1875 lasting from 8:45 to 11:35 p.m. con- 

 tained 275 specimens. Expressing these numbers according to hour-hauls 

 they are 18, 7371, and 97. Hence bettveen 26 minutes and 1 hour and 5 min- 



