FAUNA AND FLORA OF THE SEA BOTTOM. 1 23 1 



This temperature is exceeded at Woods Hole during that portion of the year 

 between June 3 and October 1 2 (diag., pi. cxxiii) . It thus appears that the sum- 

 mer conditions of temperature, such as obtain in the vicinity of Woods Hole 

 during the months of June, July, August, and September, do not directly affect 

 the western half of Vineyard Sound, and in only a hmited degree the lower end 

 of Buzzards Bay. 



A few words are necessary here regarding the hydrography of this section 

 of the New England coast. As is well known, the Gulf Stream courses in an 

 approximately northeasterly direction, at a distance of about 100 miles south 

 of Long Island, Marthas Vineyard, and Nantucket (fig. i) . That this great body 

 of warm water must affect the temperature of the surface strata, at least in Vine- 

 yard Sound and Buzzards Bay, is rendered probable by the fact that large masses 

 of the boating Sargassum, or "gulf weed," with their attendant animal life, are 

 driven thither nearly every season by prolonged southerly gales. It is likewise 

 generally believed that between the Gulf Stream and the southern coast of New 

 England there passes another more or less well-defined current, having its origin 

 in the far north. That the water of this colder current is diffused by the tides 

 along its coastward margin and affects the temperature of the outlying waters 

 of our region, especially at the bottom, can hardly be doubted." 



With few exceptions, those species whose occurrence locally is confined to 

 these colder waters are known to be primarily northward-ranging types, which 

 are here near the southern limit of their distribution, so far, at least, as such 

 shallow waters are concerned. Many of these same species have likewise been 

 encountered by us at Crab Ledge, off the southeastern bend of Cape Cod, and 

 some of them likewise on the shoals to the eastward of Nantucket. Certain 

 other forms (fig. 18, 26), though elsewhere of general distribution, are absent 

 from just those waters to which these northern types are restricted. Such 

 appear to be, for the most part, southward-ranging types, which find their 

 northern limit in Cape Cod. The numerous species (fig. 5 and many of the 

 others) which are of general distribution throughout the waters of the region, or 

 which, at least, do not appear to be restricted as regards the temperature of their 

 medium, are more commonly either species with an extended range in both direc- 

 tions up and down the coast or with a southward range only. The truly north- 

 ern types are less likely to show such a general distribution in Vineyard Sound 

 and Buzzards Bay. It is impossible to state at present how the temperature 

 factor is effective in limiting the distribution of species locally. Our thermomet- 

 ric determinations seem to show that the temperature of those waters which 

 immediately join the ocean is lower than elsewhere for probably not much 

 more than half of the year, the difference being greatest during the summer 



"See report by Libby in Bulletin of the U. S. Fish Commission, vol. i.x, 1889 (1891) p. 391-459; 

 also address before the Fourth International Geographical Congress, London, 1895. It must be added, 

 however, that the existence of such a cold current off the New England coast is now questioned by 

 some authorities. 



