1914] Esterly: Ctenophora of tJie San Diego Begion 88 



There is nothing apparent in our data to show why August should 

 be the best season, but, regardless of that, it can be seen that tempera- 

 tures above 18° (table 6) and salinities ranging from 33.61 to 33.75 

 (table 9) are most favorable. The interaction of the effects of tem- 

 perature and salinity is shown in a general way in table 10, in which 

 are considered the hauls made at favorable (33.61-33.75) and unfavor- 

 able (33.60 or less, and 33.76-33.85) salinities and at the temperature 

 groups as shown. 



TABLE 10 



Distribution of PleurobracMa at the Surface, at or Below, and Above 18° 



Summer Months 



I. Salinities Eanging From 33.61 to 33.75 



No. 

 Temperature Total. 



At 18° or below 31 

 Above 18° 38 



of hauls : 



Success. 

 A B 

 1 

 15 



No. of 

 Total. 

 C 

 26.2 

 32.5 



' hours : 

 Success. 

 D 

 0.25 

 9.7 



No. of animals: 

 Total. Per hour. 

 E F 

 1 0.04 

 3177 97.7 



Frequency : 

 Haul. Time 

 G H 

 3 1 



40 30 



II. 



Salinity 3 



;3.60 OR 



Less, and 



From 33.76 to 33.85 







At 18° or below 24 



4 



19.5 



2.5 



26 1.3 



17 



13 



Above 18° 24 



3 



19.4 



3.5 



269 14. 



12 



18 



The table is practically self-explanatory, and shows that, no mat- 

 ter what groups of salinities are considered, the collecting was about 

 equally divided between favorable and unfavorable temperatures. 

 This eliminates the possibility that successful collecting at the favor- 

 able salinities is due to the prevalence of favorable temperatures. 

 There is a range of favorable salinities but more animals are obtained 

 above 18° than below, regardless of the salinity. The cause of the 

 rarity of specimens in part II of table 10 cannot be prevalence of 

 supposedly unfavorable temperatures. 



Winter hauls for which salinities are known are so few that their 

 consideration is omitted. 



It might be expected that the ctenophores execute diurnal move- 

 ments as do the chaetognaths and copepods, but an examination of 

 our data does not lead to very certain results in that regard. Table 

 11 brings together the surface hauls as arranged to show the abund- 

 ance through the day by two-hour periods. 



