PLANKTON OF THE GULF OF MAINE 271 



but it is not clear how continuously reproduction proceeds throughout the summer 

 and autumn or whether the definite wave of propagation from September to October, 

 which the catches for those months suggest, actually takes place. 



Economic importance. — Numerically, P. parvus usually forms only a small frac- 

 tion of the catches of copepods in the Gulf of Maine, the maximum percentage 

 recorded for any station east and north of Nantucket being only 30 per cent in 

 one instance (station 10303). The averages for the area thus limited have been 

 about 1 1 per cent for March, 3 to 5 per cent for April to June, 15 per cent for August, 

 and 6 to S per cent for September and October. Therefore, owing to its small size, 

 it can never be of much importance as fish food within the gulf; but the shoals 

 which we have encountered in the shallows off Marthas Vineyard (station 10332) 

 may serve as a large item in the diet of the smaller and young fishes there. This may 

 also apply at times outside the continental edge off Georges Bank, where P. parvus 

 constituted 30 to 50 per cent of the copepods at two stations on February 22, 1920 

 (stations 20044 and 20045). 



Parathalestris jacksonl (Scott) 



The localities where this species has been taken (assembled by Sars, 1903-1911) 

 are mostly Arctic and exclusively coastwise, including the polar islands north of 

 Grinnell Land, Franz Josef Land, and the north coasts of Norway and Finland. He 

 found it occasionally on the west and south coasts of Norway, the latter being the 

 most southerly station for it previously reported. 



Doctor McMurrich lists Parathalestris jacksoni occasionally between December 28 

 and January 20 at St. Andrews, New Brunswick; more frequently (about 44 per 

 cent of the hauls) from January 20 until mid-May, but not at all during the summer 

 or autumn. The greatest frequency — late winter and spring — falls during the 

 coldest season, which corresponds to its Arctic nature. 



Probably P. jacksoni will be found all around the coast line of the Gulf of Maine 

 in similar situations and in the littoral zone generally to Cape Cod, but not farther 

 south except as a stray. 



It was never sufficiently numerous at St. Andrews to suggest that it has any great 

 importance in the economy of the estuarine waters of the gulf, much less in the 

 offshore parts of the latter, where it has not yet been found. 



Phyllopus bidentatus Brady 



This species, first described (Brady, 1883) from a single specimen from the south 

 Atlantic off the mouth of the Rio de la Plata in a haul from 2,650 fathoms, has since 

 been recorded by Giesbrecht (1892) from the eastern equatorial Pacific, from the 

 Gulf of Guinea at a depth of 5 fathoms at night and 360 by day by T. Scott (1894) ; 

 at San Diego, Calif., by Esterly (1905) ; in the Malay Archipelago by A. Scott (1909) ; 

 and off the west coast of Ireland by Thompson (1903), Wolfenden (1904), and Farran 

 (1905); but in subsequent publications (Farran, 1908; Wolfenden, 1911) the last 

 two authors have referred their Irish specimens to two new species since described 

 by Farran (1908) from that same region under the names belgse and impar. 

 75808—26 18 



