246 bulletin: museum of comparative zoology. 



I 



Tropical organisms have rarely been found in the plankton in the 

 Gulf of Maine, the only examples, from previous Grampus cruises, 

 being as follows: — Thysanoessa grcgaria at several localities (1914b, 

 p. 411), Salpa fusiformis and PJiysoj^hora hydrostatica near German 

 Bank, Salpa mucronata off Cape Cod, and in the northeastern part of 

 the Gulf in the summer of 1912 (1914a, p. 103, 121 ; 1915), and Salpa 

 tilesii in Massachusetts Bay, in December, 1913. To this brief list 

 the cruise of 1914 adds the following: — Rhincalanus in the southeast 

 corner of the Gulf (Station 10225) and Thysanoessa grcgaria (p. 282) 

 in its western side (Station 10254), on Brown's Bank (Station 10228) 

 and in the Northern Channel (Station 10229). In 1915 Rhincala- 

 nus was detected twice in the northeastern corner of the Gulf in May 

 (Station 10272, 10273): Physalia once in the Eastern Basin (near 

 Station 10288) ; and even more interesting, a bit of Gulf weed (Sargas- 

 sum) was picked up on German Bank in September (Station 10211). 



Three other forms, the copepods, Pleuromamma and Eucheirella, 

 and a pteropod, Diacria trispinosa (1915, p. 302) while oceanic- 

 Atlantic rather than typically tropical, (Scott, 1911; Cleve, 1900); 

 may be classed in the latter category so far as the Gulf is concerned, 

 since they undoubtedly enter it from the inner edge of the Gulf 

 Stream, and, judging from their rarity, have not been able to establish 

 themselves there. Eucheirella occurred twice in 1912, (1914a, p. 

 116); twice in 1913; twice in the Gulf proper in 1914; twice in 1915 

 (Stations 10270, 10310, a total of four specimens): Pleuromamma 

 was taken once in 1913 (1915, p. 288): Diacria once in 1913 (1915, 

 p. 302).  



Judging from these records, visitors from the ipher edge of the Gulf 

 Stream may be expected anjywhere in the Gulf, at any season. But, 

 as the chart (Fig. 80) shows, they have been encountered most fre- 

 quently in its eastern part although fewer hauls have been made there 

 than in the west, i. e., just where hydrography is most influenced by 

 the influx of ocean water (p. 238). 



The rarity of warm water animals in the Gulf of Maine contrasted 

 with the very rich tropical fauna which inhabits the inner edge of the 

 Gulf Stream only a short distance outside the continental shelf, is 

 fundamentally due to their inability to survive, or reproduce in the 

 low temperatures of the coast water. But their failure to appear 

 there in gre0.ter numbers, sporadically or seasonably, as they do off 

 the southern coast of New England, is evidence that the indraught 

 of offshore water into the Gulf, is not from the Gulf Stream proper, 

 but from the zone of mixed water along its inner edge (p. 239). 



