262 



November-May; females with eggs, only in February- April ; and 

 a female with attached spermatophore, in March. Nauplii appear 

 in greatest numbers in April-May, attaining 2,862 perm. 3 April 24, 

 1896, but they rarely rise* above 400 per m. 3 outside of this vernal 

 period, and are found only in very small numbers in December- 

 March. It appears from our data that the breeding season is prin- 

 cipally in April-May. 



Cyclops albidus Jurine. Average number, 113; in 1897, 136; in 

 1896, 33; and in 1894, but 10. A discussion of the variation and 

 synonymy of this species has been published by E. B. Forbes ('97). 

 The species is numerically least important of the dominant members 

 of the genus in our plankton. It was recorded in all months but 

 December and February, but its season is practically confined to 

 April-October, the only exceptions being three records in small 

 numbers in January, March, and November, and two of larger 

 numbers (300 and 200) in the higher temperatures of the delayed 

 autumn of 1897. There is a tendency toward a summer minimum 

 in June- July, with pulses of greater amplitude in April-May and 

 again in August-October. In these months the percentage of 

 collections containing C. albidus is highest, being respectively 55, 

 50, 38, 56, and 53 per cent., and these are the only months in which 

 the numbers per m. 3 rise above 600. The highest numbers recorded, 

 2,862 and 2,400, occurred respectively on April 24, 1896, and 

 October 5, 1897. 



Although C. albidus is found in the extremes of temperatures, 

 it shows a decided increase after temperatures pass 60 in the 

 vernal rise, and falls off immediately after the autumnal decline 

 passes this point. With high temperatures continued into October, 

 in 1897 we find it continuing in larger numbers. On the other 

 hand, during maximum summer heat (about 80) numbers, as a 

 rule, fall below 300 per m. 3 The temperature optimum thus appears 

 to be in the neighborhood of 70. The three greatest pulses re- 

 corded, occur respectively on April 24, 1896, at 72; on April 26, 

 1898, at 57-, and on October 5, 1897, at 71. 



The numbers are too small to exhibit very clearly the phenome- 

 non of recurrent pulses, though the vernal and autumnal pulses are 

 usually well defined, and in the stable conditions of 1897, August, 

 September, October, and November pulses may be traced. 



