348 BULLETIN OF THE BUREAU OF FISHERIES 



Ptychogena lactea, A. Agassiz 



The importance of this Arctic hydroid medusa in the Gulf of Maine as an indica- 

 tor of water from the north has been emphasized in an earlier chapter (p. 59) . I 

 need merely list here the following records of its occurence: 



Massachusetts Bay at Nahant, "where they have only been found during a 

 single fall, and then only for a few days, when they seemed quite abundant" (A. 

 Agassiz, 1865, p. 139); eastern basin of the gulf, May 6, 1915 (station 10270); 

 German Bank the next day (station 10271) , one specimen at each station; and several 

 examples near Lurcher Shoal on the 10th of the month (station 10272). 



The presence of this Arctic medusa in Massachusetts Bay in the autumn of 1863, 

 as recorded by Agassiz, contrasted with the fact that we have since found it only in 

 spring at the time the Nova Scotian current is at its maximum, and in the opposite 

 side of the gulf, is an interesting phenomenon and one yet to be accounted for. 



The nearest locality record for Ptychogena to the northward with which I am 

 acquainted is from the neighborhood of Halifax, Nova Scotia, where it was taken by 

 the Challenger (Haeckel, 1881). 



Ptychogena lactea is Arctic and circumpolar. It has been recorded from several 

 localities along the west coast of Greenland and in Barents Sea between northern 

 Norway and Spitzbergen, from Franz Josef Land, from the Kara Sea near Nova 

 Zembla, from Bering Sea, and from the Sea of Okhotsk. Its most southerly records 

 are the Gulf of Maine in the western side of the Atlantic, between Scotland and 

 Iceland in the eastern side, and the east coast of Hokaido, Japan, in the Pacific 

 (Bigelow, 1913; Kramp, 1919, p. 37). 



Mitrocoma cruciata (A. Agassiz) 



Mitrocoma cruciata, Staurophora, and Phialidium are the only hydroid medusae 

 that we have found generally distributed in the open gulf at any season. Mitro- 

 coma is further interesting because it was not seen from the time it was first de- 

 scribed by Alexander Agassiz (1865) from Nahant, Mass., many years ago, until 

 the Grampus rediscovered it in the gulf in July, 1913 (Bigelow, 1915, p. 316). 

 Although the development of this species has not been traced, there is every reason 

 to suppose that its hydroid stage, like that of its close relative, the Mediterranean 

 M. annx, is a Cuspidella. 



In the Gulf of Maine Mitrocoma is a spring species. In 1920 the Albatross 

 towed specimens occasionally from February 23 (our earliest seasonal date for it) 

 until May 4 (stations 20048, 20091, 20105, 20106, and 20120). In 1915 we found 

 it not uncommonly in May and June (stations 10270, 10271, 10278, 10282, 10286 

 to 10288, 10290, 10291, and 10293). A. Agassiz's record was also for June. We 

 have one July record of it in 1913, just noted, one in 1915 for July 15 (station 

 10301), one for August 4 (station 10303) and others for the 12th and 14th in 1914 

 (stations 10246 and 10250) ; but the middle of August apparently marks the end 

 of its season of occurrence, for we have not found it on any of our cruises later 

 in the season. Thus, its period of abundance precedes and somewhat overlaps 

 that of Phialidium. The localities of capture are widely distributed in the 



