PLANKTON OF THE WOODS HOLE REGION 143 
prevailed. The summer forms from the Gulf Stream taken in 1922-23 were 
Pontella pennata, P. meadii, Anomalocera patersoni, Microsetella rosea, Setella gracilis, 
and Thawmaleus claparedii. 
No distinct division can be made dividing the summer forms from the winter 
ones. Figures 40, 42, 44, etc., show clearly how much the seasonal distributions of 
the various species overlap each other. Certain forms, such as Centropages hematus, 
appear as early as August and remain until May. As the breeding season is in 
December and January, they are considered to be true cold-water forms. 
The winter copepods may roughly be divided into four groups: (a) Those 
northern species that remain in deep water or north of Cape Cod during the sum- 
mer, entering this region every winter in great numbers, (6) the young of the winter 
species, (¢) northern oceanic forms occasionally finding their way in, @) Har- 
pacticide, usually  acci- 
dental members of the 
he 
%.5: 
V.S. 
Fic. 43.—Occurrence of Centropages 
in surface collections from June to 
December, 1922. ———, Cenitro- Be 
pages typicus; ==-==, C. hematus; Fic. 44—Occurrence of Centropages in surface collections of 1923. 
—e—, C. hematus (immature ———, Centropages typicus; , C. hematus;i—eeo—, C. typicus 
forms) (immature form); —.—, C. hematus (immature form) 
plankton, but in a few cases rising to the surface during the breeding season. 
Three copepods are usually characteristic of all winter plankton—Pseudo- 
calanus elongatus, Temora longicornis, and Centropages hematus. During the 
years 1922 and 1923 almost no specimens of Temora appeared. This is very 
unusual, for all samples of past years taken at this season are literally filled with 
them. As they appear in the greatest numbers in February, March, and April, 
the unusually cold weather of the spring of 1923 (fig. 5, opp. p. 100) may have affected 
them as it has many of the other animals. The young of Pseudocalanus and 
Centropages became so abundant in January and February that they far out- 
numbered the adults, a condition which was never found among summer forms. 
A few immature Temora were noted, but their appearance was not common. 
Northern species are sometimes plentiful in the waters of Vineyard Sound and 
often appear in surface collections in Great Harbor. Calanus finmarchicus is the 
most common of these cold-water forms. Metridia lucens, Eurytemora herdmant, 
and £. hirwndoides were taken often during the spring of 1924. No other northern 
copepods to my knowledge have ever been recorded from Woods Hole. 
