PLANKTON OF THE GULF OF MAINE 



273 



P. robusta, two stations outside the continental edge between the latitudes of 

 Delaware Bay and New York, July, 1913 (stations 10064 and 10071); one station 

 outside the edge off Shelburne, Nova Scotia, July 28, 1914 (station 10233); one 

 Canadian fisheries expedition station outside the continental edge and three over 

 the outer part of the shelf off Nova Scotia, July, 1915 (Willey, 1919) ; and one Michael 

 Sars station east of the Grand Banks (Murray and Hjort, 1912, p. 654). 



P. xiphias, one station outside the continental edge off Delaware Bay, July 20, 

 1913 (station 10071). The Canadian fisheries expedition of 1915 had it at one 

 June station in deep water off the mouth of the Laurentian channel, one July station 

 near Sambro Bank and one outside the continental edge off Cape Sable (Willey, 1919) ; 

 it was also listed by Sars from the same Michael Sars station east of the Grand 

 Banks which yielded gracilis and robtbsta (Murray and Hjort, 1912, p. 654). 



It is probable that when the ranges of these four Pleuromammas are better 

 understood it will be found that all of them are universal away from land over the 

 temperate and tropic latitudes of all oceans. Off the eastern coast of America, the 

 continental edge and the outer part of the continental shelf would seem their normal 

 inshore boundary, along which all of them may be expected in the warm, highly 

 saline waters of the inner edge of the so-called "Gulf Stream" as far north as the 

 Grand Banks: but the presence of abdominalis in the Gulf of St. Lawrence and the 

 Gulf of Maine records to be mentioned next show that on occasion they may drift 

 into distinctly neritic situations. 



One other species of the genus, P. boreale, is to be expected in the Gulf of Maine, 

 having been found by the Canadian Fisheries Expedition of 1915 at five stations off 

 Nova Scotia (Willey, 1919) side by side with the others; but as yet it has not been 

 detected in the Gulf of Maine towings. 



The several Pleuromammas, like other planktonic animals which are purely 

 immigrants, and uncommon ones, in the Gulf, have most often been found in the 

 eastern side — that is, nearest their path of entrance (fig. 82) — and in the southwest 

 part, which they may fairly be assumed to have reached via the anticlockwise eddy 

 which dominates the circulation of the gulf. 



If the data so far obtained are fairly representative, abdominalis (only one 

 record) is the least common of the four species in the Gulf of Maine, whereas it is 

 the only Pleuromamma yet reported from the Gulf of St. Lawrence and the most 

 common at San Diego (Esterly, 1905). Pleuromamma has been represented by 

 scattering specimens in the Gulf of Maine tows, its numbers per square meter working 

 out as follows for the spring stations of 1920: 



