28 University of California Publications in Zoology [Vol. 13 



at this time that it will not be entered into. What follows deals with 

 the relation between abundance and external factors without regard 

 to the stage of growth of the animals. 



The Pleurohrachia of this coast is probably a variety of P. pileus 

 of the Atlantic. Bigelow (1912, p. 374) states that in his opinion 

 hachei is not the same as pileus, but Mayer (1912, p. 13) says pileus 

 is ' ' commonly called hachei on the Pacific Coast. ' ' The Atlantic form 

 seems to be found mostly in cold water. Mayer states that it is found 

 off southern New England early in April and disappears as the water 

 grows warmer so that it does not occur there during the summer. It 

 is found, however, in vast swarms during the summer in the cold 

 water of Maine and Nova Scotia. Dr. Bigelow writes in a letter that 

 the surface temperature off Portland, Maine, during July and 

 August ranges from 14° to 15.5° and drops to 10° off Eastport. He 

 has met swarms of Pleurohrachia in the summer at 14° and in Janu- 

 ary at 7° in Massachusetts Bay and has found P. hachei at Acapulco at 

 about 27°. According to Steuer (1910, pp. 571, 572), Pleurohrachia 

 pileus was most abundant in the Adriatic from January through April 

 from 1900 to 1904. Prom 1898 to 1904 this ctenophore was of irregu- 

 lar occurrence during June, July, August, September and October, 

 and was not taken at all during August. Such general observations 

 as have been set down indicate that Pleurohrachia is typical of cold 

 water, and Steuer states (p. 485) that pileus is one of three character- 

 istic ctenophores of the polar region. It seems certain that the tem- 

 peratures at which Pleurohrachia is particularly abundant here and 

 in the Atlantic are markedly different, but a detailed comparison is 

 hardly possible at this time. 



TABLE 5 



Total Number of Hauls, Number of Successful Hauls, Numbers of Pleuro- 

 brachia, in Hauls During Each op the Summer Months at Temperatures 

 Above 16°. Left-Hand Figures, Total Hauls; Center Figures, Successful 

 Hauls; Eight-Hand Figures, Numbers of Animals. 



Temperat 



ures 





June 







July 









August 

 



September 



October 



A 



16?1-17° 



27 



2 



^ 



9 



3 











1 











r ^ 







17?1-18° 





27 



2 



2 



1 







11 































18?1-19° 





11 



3 



110 



9 



2 



11 















3 



1 



250 



2 



19?l-20° 





2 



1 



253 



12 



1 



1 



14 



10 



3868 



1 



1 



1 



12 



20 ?1 and 



more 















11 



2 



21 



24 



12 



2556 



1 











2 



