PLANKTON OF THE GULF OF MAINE 
165 
more likely that constantly high temperature, not high salinity, is its outer barrier 
off eastern North America, and bars it from the warmer parts of the Atlantic in 
general. Within these wide limits, however, Euthemisto is very tolerant of varying 
salinity, both in the western Atlantic and in the eastern. 
At times and places where Euthemisto is abundant it probably serves as a valu- 
able food for pelagic fishes in the Gulf of Maine, though little information is avail- 
able. In Irish seas Tattersall (1906) found it forming a very large part of the food 
of two of the principal food fishes — herring and mackerel — as well as of the sea 
trout, while at times it forms the chief sustenance of the long-finned tuna ( Germo 
alalunga) off the French coast (Le Danois, 1921). Euthemisto, in its own turn, 
is extremely destructive to copepods and to other small planktonic animals (p. 107). 
Before closing the brief account of this genus, I must emphasize our failure 
to find even a single specimen of the arctic Euthemisto ( E . libellula) within the 
limits of the Gulf of Maine. Certainly it does not reach it unless as the rarest of 
stragglers. 
Other hyperiids 
The two species of Euthemisto are the only hyperiids that are of any numerical 
importance in the plankton of the Gulf of Maine. Their relatives, Hyperoche and 
Hyperia (similarly boreal in faunistic status), have been taken at several stations 
but always in small numbers. 
Hyperia 
Hyperia is represented locally by two species — galba and medusarum — both of 
which usually live commensal with the large medusae Aurelia or Cyanea. This is 
not invariably the case, however, for Hyperia has repeatedly appeared in the catches 
of the tow nets at stations where no medusae were taken or seen — for example, on 
German Bank, August 14, 1912 (Bigelow, 1914, p. 103). Associated with their 
occasional independence of the medusfe we have found one or other species of the 
genus widely distributed in the northern half of the gulf, over deep water as well 
as shallow, but our nets have never yielded more than four or five specimens of 
Hyperia at any one station. Hyperia medusarum has been taken both in summer 
and in winter, but H. galba has so far been taken only in July and August. 
In the case of animals as comparatively scarce as Hyperia is in the Gulf of 
Maine, captures in tow nets are so largely a matter of accident that they do not give 
a reliable picture of the numerical strength of the species in question from season 
t'o season and from place to place. It seems, however, that Hyperia was decidedly 
more numerous in 1913, when we found it at some half dozen stations in the gulf 
(Bigelow, 1915, p. 279), than in the summer of 1914, when it was not found at all 
at the same localities and season (Bigelow, 1917, p. 289), or in 1915, when only odd 
individuals were taken during the summer. 
Hyperoclie 
Hyperoche tauriformis 90 has appeared rather more commonly in our tow net- 
tings than has either species of Hyperia, having been taken at 10 stations in the 
so In an earlier report (Bigelow, 1915) this amphipod appears as “ H. kroyeri Bovallius,” but recent students of the group — 
e. g. Teseh, (1911) and Tattersall (1906) — agree that while it has passed most often as “kroyeri” or as “ abyssorum” Boeck, its cor- 
rect designation is “H. tauriformis” Bate and Westwood. This name is accepted here for the sake of uniformity, the question 
not being of specific identity but simply of the distribution of the only species of Hyperoche known to exist in northern seas. 
8951—28 12 
