416 BULLETIN OF THE BUREAU OF FISHERIES 



occurs in any numbers, and at all seasons, 42 both in the inner parts of the gulf, on 

 Georges Bank, on Browns Bank, and off southern Nova Scotia (Bigelow, 1917, p. 

 323). It has been lacking, or at least so rare as to be overlooked, whenever diatoms 

 swarm, in which it parallels the more abundant species, tripos and longipes; occasion- 

 ally, also, among catches of Ceratium plankton. However, no more definite seasonal 

 fluctuation in abundance has been established for it in the Gulf of Maine, nor any 

 regional concentration. Notwithstanding its nearly universal distribution in the 

 gulf and almost constant occurrence there, it seldom rivals the tricornuate forms of 

 Ceratium in abundance, the only instance of this sort so far recorded being that 

 C. tripos and C.fusus were about equally numerous in the center of the gulf on August 

 10, 1913 (Bigelow, 1915, p. 334, station 10090). 



The sporadic occurrence of the tropical species, C. macroceras, in the inner 

 parts of the gulf has already been alluded to (p. 393). C. bucephaZum (Paidscn, 190S, 

 p. 77, fig. 100) has also been recognized once in early spring (mouth of the Bay of 

 Fundy, station 20079, March 22, 1920); likewise off the southeast face of Georges 

 Bank on February 22, 1920 (station 20044), and south of Marthas Vineyard, Novem- 

 ber 11, 1916 (station 10406). 



Other peridinians 



Only two other genera of pcridinians have so far been definitely recognized in 

 the Gulf of Maine — Peridinium and Dinophysis — though others doubtless occur. 

 The former has been noted in practically every summer sample in which Ceratium 

 occurs (Bigelow, 1915, p. 334); that is, it is practically universal in the gulf except 

 in regions and at times where diatoms flower abundantly, (and even there it may be 

 present but overshadowed by their masses) or when the plankton is so scanty that 

 it may have been overlooked, though actually present, as, for example, at several 

 of our stations in the early spring of 1920. Peridinium is usally a minor element in 

 the phytoplankton ; far less numerous than its companion genus Ceratium. In 

 summer and early autumn the only exceptions to this rule have been on th« western 

 part of Georges Bank, July 20, 1914 (stations 10215 and 10216); near Mount Desert 

 Island, September 15, 1915 (station 10317); and off Penobscot Bay, October 9 of that 

 same year (station 10329), where the genus as a whole (represented by several species) 

 was nearly as numerous as either species of Ceratium. Peridinium is relatively 

 even less important in early spring, as exemplified by our cruises of March and April, 

 1920, when it was represented by few or occasional examples only, though it occurred 

 at about half the stations, distributed over the gulf generally 43 except in the rich 

 diatom centers. In May of 1915, however, Peridinium not only occurred at every 

 station where Ceratium was detected, but rivaled the latter in abundance in the 

 eastern side of the gulf (fig. 115, stations 10270, 10272, and 10273). 



As it was again an important element in the plankton of the southwestern part 

 of the basin and of the South Channel on May 17, 1920 (stations 20127, 20128, and 



" For records of its occurrence in the summer hauls of 1913 and 1914 see Bigelow, 1915, p. 333, and 1917, p. 323. During the 

 autumn of 1916 it was recognized at stations 10400 to 10406; during the spring of 1920 at stations 20044 to 20046, 2004S, 20049, 20052 to 

 20055, 20057, 23013 to 2J015, 20067, 20008. 20O70 to 20074, 20077, 20030, 20086, 20087, 20093, 20096 to 20098, 20101. 2010S, 20111, 20112, 200116, 

 20118, 20125, and 20128; and at all the stations during December, 1920, and January, 1921 (stations 10488 to 10502). 



<> Recorded for stations 20014, 20045, 20046, 20048, 20057, 20060, 20064, 20065, 20068, 20071, 20074, 20075, 200S-0, 200S6, 200SS, 200S9, 

 20096, 20111, 20118, and 20119 for these months. 



