98 BULLETIN OF THE BUREAU OF FISHERIES 
if this is not true, Verrill and subsequent authors, including Bigelow (1914-1922), 
found that the coastal water temperatures north and east of Cape Cod were very 
much lower in summer than those south of it. None of the planktonic animals 
common north of the cape appear south of itinsummer. In winter, however, the 
cape does not form a barrier for the neritic plankton, which often appears at Woods 
Hole in great abundance. 
The Gulf Stream lies about 85 nautical miles off the Massachusetts coast, 
just beyond the end of the Continental Shelf. Between this warm area and the 
mainland there is a broad belt extending from the north. Some consider this to be a 
continuation of the Labrador current and attempt to explain faunal distribution 
on that basis. Others consider it to be mainly a contrast belt between the warm 
littoral zone and the Gulf Stream. According to the latter viewpoint, the Labrador 
current does not extend south of Newfoundland. No matter which theory is 
correct it is evident that this broad belt is affected on one side by the southerly 
winds and on the other by the unusually strong tides of this region. Any forms, 
then, that have blown in from the Gulf Stream will be carried farther mland by the 
moving water. This peculiar alliance of wind and tide probably explains why 
much tropical plankton, which is taken so often in this locality, occurs at no other 
points along the coast. 
Woods Hole also forms the northern limit of most of the southern boreal 
pelagic animals. Many copepods and celenterates, of which Mnemeopsis is a 
striking example, occur often in Great Harbor but never farther north along the 
coast. Thus, it is clearly evident that Woods Hole is a very unsatisfactory spot to 
work out the characteristic pelagic fauna of the north Atlantic coast region, for not 
only northern and southern boreal types appear with the littoral plankton at certain 
seasons, but the Gulf Stream and other oceanic forms are likely to be carried in at 
any time. Again, the swift currents rushing through the passage produce local 
peculiarities in the plankton. However, if we desire to study the conditions at 
Woods Hole as a special problem and try to understand the conglomeration of 
faunas, their interrelations, and the factors governing their appearance and dis- 
appearance it becomes highly interesting and instructive. 
SALINITY AND DENSITY 
The salinity at Woods Hole normally varies comparatively little throughout 
the year. No streams of importance empty into Great Harbor, and as all the 
larger rivers of Buzzards Bay are situated at the upper end the salinity of the 
southern area is not sufficiently different from that of the sound to have any appre- 
ciable effect on the plankton. 
Titrations made almost daily from July until October, 1922, during the flood 
tide (Table 1) indicate that the water entering Great Harbor is of a slightly lower 
salinity than that of Vineyard Sound, found by Bigelow (1915) to be 32.2 per mille 
in August, 1913, and by Sumner (1913) to be 32.2 per mille in August, 1906. In 1922 
the average salinity at the Fisheries dock for late July and August was 31.57 per 
mille, and for September and early October, 31.03 per mille. 
