seem to indicate that the nauplii had been abundant earlier in the 

 month and were on the decline. The importance of this will appear 

 later. The nauplii increased rapidly in June and Jiily, reaching 

 a maximum of 32 per liter for the season in late July. There was a 

 sharp decline to 11 per liter in early August, followed by an increase 

 to 25 per liter. Thereafter they waned and reached a minimum for the 

 season in late October, 



The genera Limnocalanus, Epischura, Bosmina, and Leptodora 

 appeared in comparatively insignificant numbers. Limnocalanus 

 was extremely rare. It was absent from 3 of the 8 stations, and 

 appeared nowhere after May. The highest count recorded for any 

 station was 0,2 per liter, Epischura was present in small numbers 

 throughout the season. The highest counts at any station were 2 per 

 liter; these occurred in June, July, and August, At no time did it 

 average 1 per liter for the whole section. Bosmina was the most 

 abundant of the four genera mentioned. It was present in small 

 numbers in late May, increased somewhat in June but almost dis- 

 appeared in late July and early August. A second period of increase 

 followed, and judging from three series taken in October, it was in- 

 creasing when sampling was discontinued. The highest coiint recorded 

 was 7 per liter but it was usually less abundant than 1 per liter, 

 Leptodora was taken frequently from June through September but it 

 never attained abundance of 1 per liter. 



Season of 1930 



Plankton studies were begun April h in 1930 and discontinued 

 October 3. The results obtained are shown in Table 70, and partially 

 in Fig. 20, 



In early April Diaptomus was present in small numbers and 

 increased only slightly to 2 per liter ty late April. In early 

 May it had increased to 9 per liter, and reached a maximum for the 

 season (10 per liter) in late May. The count for early June was 

 reduced to h per liter but increased in late June to 8 per liter. 

 Thereafter Diaptomus declined, and in August and September was an 

 unimportant member of the plankton. Thus there were two periods of 

 abundance, the first in May, the second in late June - early July, 



Cyclops increased somewhat more slowly than Diaptomus in 

 April and early May, but by late May it was the more abundant of 

 the two. It continued to increase in June, reaching a minor peak of 



219 



