Cyclops. 457 



Cyclops leucJcarti Sars., Cyclops pulchellus Koch., and Cyclops 



orevispinosus Herrick. 



The three species of Cyclops named above stood second in num- 

 ber among the pelagic Crustacea of July, averaging 30.5 per 

 cent, for the entire month and increasing from In per cent, in 

 Period I to 40.5 per cent, in Period II. They were counted to- 

 gether, as no considerable difference in their vertical distribu- 

 tion appeared, and as it was difficult or impossible to distin- 

 guish the species from each other under a low power of the 

 microscope. Observations made later in the year seem to show 

 that Cyclops leucJcarti was more abundant at greater depths than 

 was Cyclops brevispinosus, but no sufficient number of observa- 

 tions have been made to warrant a positive opinion. In all cases 

 Cyclops brevispinosus was the most abundant, and ordinarily 

 there were several times as many of that species as of the others. 



Number of Cyclops. — The average number of Cyclops caught in 

 each series of hauls for the entire month was 2010. The area of the 

 dredge was ^ square meter, and its co-efficient probably about 

 four, indicating a number of Cyclops of 200,000 per square meter 

 of surface. The greatest number obtained was 5460 (J. 27; 6 

 a. m.). The smallest number was 176 (J. 10; 8 p. m.). The 

 variations in successive hauls were somewhat smaller than was the 

 case in Diaptomus. The greatest variations observed in succes- 

 sive catches were: 



July 27, 3 A. M 2945 



July27,6A. M 5460 



July27,9A.M \ 3036 



This exceptionally large catch of Cyclops coincided with a 

 similar large number of Diaptomus, and the number found was 

 unusually large at all of the 4 upper levels (0-12 m.). The least 

 variation in number was obtained in 4 consecutive catches on 

 July 18, from noon to 9 p. m. , the numbers being 1384, 1395, 

 1381, and 1397, respectively. It may, however, be added that 

 in these 4 catches the distribution in the different levels was 

 quite different. The number caught in the 0-3 m level ranged 

 from 498 to 906; in the 3-6 m. level, from 222 to 540; in the 

 6-9 m. level, from 140 to 336. Thus while the total number of 



