BIGELOW: COAST WATER EXPLORATION OF 1913. 335 



Gulf of Maine plankton, 1912 and 1913. 



The summer plankton of the Gulf of Maine was of the same general 

 type in 1913 as in 1912 (1914a). The lists of copepods, far the most 

 important constituent of the macroplankton, are practically the same 

 for the two years, the most numerous and most regularly occurring 

 species was Calanus finmarchicus. But Calanus hyperboreus, taken 

 only once in 1912 occurred at four stations in 1913, once in large 

 numbers (p. 286); Eucheata norvcgica was, likewise, taken more 

 regularly in 1913, where it was practically universal in the deep waters 

 of the Gulf (fourteen stations) than in 1912 (nine stations); and 

 Metridia longa is recorded for the first time from our waters. Anoma- 

 locera was taken more regularly in 1913 than in 1912, but in this case 

 the difference is probably apparent rather than real, due to different 

 types of nets used on the surface, where Anomalocera is most abun- 

 dant. Euchirella rostrata, singularly enough, was taken twice in each 

 year, once on each side of the Gulf. 



In the case of the hyperiids the difference between the hauls of the 

 two years was much greater, because Euthemisto hispinosa, a species 

 common in the centre of the Gulf in 1913 was not found at all during 

 the preceding summer. Its history during the year in Massachusetts 

 Bay is as follows: — absent there during the summer of 1912, it must 

 have appeared in the early autumn, for it was about half as numer- 

 ous as compressa in November (1914b). But later in the season it 

 was proportionately rare in the hauls (six compressa to one hispinosa 

 in April) and by August, 1913, the Euthemisto component of the 

 plankton of Massachusetts Bay was once more exclusively compressa. 

 This local series of changes suggests the possibility that there may be a 

 parallel series for the Gulf as a whole, hispinosa appearing seasonally, 

 in winter and spring, to disappear again in summer. If this be the 

 case, the species must have persisted longer in 1913 than it did in 1912. 

 But the appearance of hispinosa may have been the result of an inva- 

 sion of the Gulf by this species during the autumn of 1912. In both 

 summers Euthemisto compressa was very generally distributed over the 

 Gulf. Parathemisto ohlivia, taken at two Stations (10032 and 10036) 

 in 1912, was not detected at all in the hauls of 1913. The rarity of 

 this species is interesting because of its wide distribution and frequent 

 occurrence on the other side of the Atlantic (p. 341). The remaining 

 hyperiids, Hyperia galha, H. medusarum and Hyperoche were occa- 

 sionally represented in both years. 



The only pteropod which we have found in any great numbers in the 



