PLANKTON OF THE WOODS HOLE REGION 141 
In the collections of the past year one of this tribe (Cylindroleberis mariz) 
appeared with greater frequency than any other one species, even though the 
Podocopa are much more abundant at certain spots in Great Harbor. This instance 
shows how easily wrong conclusions may be made in the study of littoral plankton if 
the bottom fauna is not clearly understood. It illustrates, also, an important 
point about the fauna of the harbor. The bottom forms dwelling here are so dis- 
tributed that they are protected from the rushing currents, although they are able 
to derive benefit from the food material carried by these waters. For that reason, 
even under unusual conditions, the benthos occurring in surface collections proba- 
bly is transported from Buzzards Bay. This is quite evident in the case of amphi- 
pods where the distribution is very well understood. Even the animals of the 
“Gut of Canso” are carried away rarely, and the ostracods become dislodged only 
when the hydroids and Fucus, to which they attach themselves, are torn from their - 
bases. 
The following ostracods were taken in 1922-23: Sarsiella americana Cushman, 
Cylindroleberis mariz (Baird), C. zostericola Cushman, Loxoconcha impressa (Baird), 
Cythereis emarginata Sars, and genus Cythereis (several species). 
COPEPODA 
Together with the Phyllopoda and an occasional euphausid or hyperid, the 
Copepoda form the only truly pelagic Crustacea of the local plankton. Except in 
the seasons of diatom maxima, they are always present in abundance. Farran 
found that whenever a species is present in sufficient numbers a distinct periodicity 
in its occurrence is noticeable. This is true at Woods Hole. Although copepods 
are always present in varying numbers, certain species are continually disappearing 
and being replaced by others. The copepods of Great Harbor may be divided 
roughly into two great groups—the summer community and the winter community. 
The summer forms may arise from three sources: (2) Annual appearance of 
local coastal species common to the region, (b) the young of these common forms, 
appearing often in large numbers during the breeding season, (c) southern oceanic 
forms blown in by winds from the Gulf Stream during the warm weather. 
The first of these sources accounts for most of the summer species. These 
may again be grouped under two headings: (1) True pelagic species and (2) bottom 
forms appearing after hard winds. The most typical summer pelagic species are 
Acartia tonsa and Centropages typicus. These form the bulk of the summer copepod 
fauna. Later in the fall Pseudodiaptomus coronatus reaches its maximum and 
outnumbers all other forms. This, however, is not a true summer species, but 
serves as a connection between the warm and cold water copepods. Tortanus dis- 
caudata serves in a similar capacity in the spring and early summer. Benthonic 
adults of the family Harpacticide are often taken in surface collections. These are 
usually found among bottom plants and alge but are capable of swimming quite as 
well as the Gymnoplea. The most common summer Copepoda are Acartia tonsa, 
Centropages typicus, Pseudodiaptomus coronatus, Labidocera estiva, Oithona similis, 
O. brevicornis, Alteutha depressa, Parategastes sphzricus, Amphiascus obscurus, 
Ilyopsyllus sarsi, and Dactylopusia vulgaris. 
