211 



numbers of that year, while the larger numbers in 1897 may be 

 attributed to the more stable conditions. The small numbers in 

 1898 do not seem to be correlated with any feature of the environ- 

 ment. 



This species has been found in every month of the year, and is 

 thus perennial in our plankton. As will be seen, however, in Table I. , 

 the most of the occurrences and a much greater proportion of the 

 individuals are found between May and October, and thus above 

 60. The same limitations are found in the other years, with the 

 exception that in 1896 there was a more continuous and larger de- 

 velopment from the last of February. In the table which follows 

 it may be noted that all of the pulses but four are at temperatures 

 above 70, and of these four none exceeds 25,000, and two do not 

 exceed 2,500. The optimum conditions for the species in our 

 waters are therefore above 70. The average temperature at the 

 time of the larger pulses is near 80. The vernal pulses are poorly 

 defined, as are likewise the autumnal ones. It is a midsummer 

 species in our waters, with its maximum in August. 



PULSES OF SYNCH^ETA PECTINATA. 



(IS) 



