412 



BULLETIN OF THE BUREAU OF FISHERIES 



Whether the summer augmentation of C. tripos, accompanied as it is by a decrease 

 on the part of C. longipes, actual as well as relative, originates as the result of local 

 propagation of the few specimens that survive the spring, or from immigration from 

 the south and west, or of both processes, is not yet clear; but in either case the central 

 deeps may be looked upon as its chief area of multiplication in the Gulf of Maine. 

 From this center it gradually expands its area of abimdance right in to the immediate 

 vicinity of the land where C. longipes decreases in abundance as the numbers of C. 

 tripos augment, just as happens offshore. 



Relative abundance of the two predominant species of Ceratium, July and August, 1914 



Station 



10213 

 10216. 

 10223. 

 10225. 

 10227 

 10229 

 10230 

 10245 

 10246 

 10248 



C. lon- 

 gipes 



50 

 38 

 21 

 9 

 34 

 21 

 60 

 105 

 62 

 29 





C . tripos 



Station 



10249 



10250. 

 10251 

 10253. 

 10254 

 10255 

 10256 

 10258 

 10264 



C. lon- 

 gipes 



13 

 32 

 US 

 2 

 4 

 

 5 

 1 

 1 



C. tripos 



47 

 2 

 1 



10 

 50 

 50 

 76 

 11 

 23 



C. tripos usually predominates near Cape Cod and in the southern part of Massa- 

 chusetts Bay by the last week in August. For example, we found 23 tripos to 1 

 longipes off the east side of Stellwagen Ledge on August 28, 1914 (station 10264), 

 while the relationship between the two species was much the same near Provincetown 

 on the 29th of the month in 1916 (station 10298). In some years, at least, this 

 practical elimination of C. longipes from the catches happens equally early in the 

 season near Cape Ann, where we found C. tripos much the more abundant of the 

 two as early as August 22 in 1914 (station 10253, five times as many tripos as longipes) , 

 but in other summers C. longipes persists in numbers in the northeastern part of 

 Massachusetts Bay long after tripos has taken its place off Cape Cod. This was 

 the case in 1915, when the former predominated off Cape Ann on August 31 (station 

 10306, 17 longipes to 2 tripos) and about equaled tripos there as late as September 29 

 (station 10320), though the latter abounded, with almost no longipes, inside Stell- 

 wagen Ledge and near the tip of Cape Cod, only a few miles distant to the south, 

 on the same day (stations 10221 and 10222). In fact, it was not until well into 

 October that tripos finally replaced longipes at our standard station off Gloucester 

 during that autumn (station 10330, October 18, 100+ tripos to 1 longipes). Prob- 

 ably the fact that O. longipes may persist in abundance in the northern side of Massa- 

 chusetts Bay long after it has dwindled almost to the vanishing point in the southern, 

 and such variations as I have just recorded in the precise date when C. tripos 

 replaces it off Cape Ann from summer to summer, are due to variations in the drift 

 flowing southward past Cape Ann, which may be expected to bring a constant supply 

 of C. longipes with it throughout the summer, for the latter continues predominant 

 over C. tripos, or at the least is a large factor in the peridinian plankton of the 

 more northerly and easterly parts of the coastal belt of the gulf until well into 

 the autumn as follows: 



