248 



bulletin: museum of comparative zoology. 



origin, i. e., the pteropod Limacina helicina, the appendioularian 

 Oikopleura vanhoffeni, and of Mertensia, associated with the Cabot 

 Current water in the Gulf in May, 1915, marks a distinct advance 

 in our knowledge. These as shown on the chart (Fig. 81) were all 

 taken just where salinity (p. 224) and temperature (p. 215) gave 

 clearest evidence of this northern water (Stations 10270, 10272), and 

 each was represented by so many specimens, that their occurrence 

 can not be looked on as accidental. The appearance of the Arctic 



1 .- . ^-^n' 



.^ ^ — 



VJ N 



.^' 



../A 



H— — 



,..#• 



'"cA", 



'tSi 



'A 



Fig. 81. — Grampus records of Arctic plankton organisms in the Gulf of Maine, 1912- 



1915. 

 H, Limacina helicina: M, Mertensia ovum: O, Oikopleura vanhoffeni. 

 Diphyes arctica is given here also (A), though its geographic origin is doubtful (p. 306). 



Oikopleura in the Gulf is especially noteworthy, since it has not been 

 recorded previously on this side of the x\tlantic south of Bafiins Bay, 

 though known in European waters as far south as the Shetland Is- 

 lands (Lohmann, 1896, 1910). Thanks to Lohmann's excellent de- 

 scriptions and figures (1896, p. 72, taf. 14, fig. 6, 7, 10; 1910, p. 15, 

 fig. 16, 17) it is easily recognized, its chief difference from the closely 

 allied 0. labradorensis being the presence of many small, dendritic, 



