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. libeUula) witliin the 

 limits of the Gulf of Maine. Certainly it does not reach it unless as the rarest of 

 stragglers. 



»&* 



Other hyperhds 



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 medusae 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 

 to 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. 



Hyperoche 



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 



"In an earlier report (Bigelow, 1915) this amphipod appears as " H. kroyeri Bovallius," but recent students of the group— 

 e. g. Tesch, (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 Wcstwood. 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. 



