1458 CRUSTACEA. 



no interval between them on the American coast. The line of 56° 

 F. has a deep northward flexure between the meridians of 35° and 

 40° west, arising from the waters of the Gulf Stream, which here 

 (after a previous east and west course, occasioned by the Newfound- 

 land Bank, and the Polar Current with its icebergs) bends again 

 northeastward, besides continuing in part eastward. The Polar 

 Current sometimes causes a narrow reversed flexure, just to the east of 

 the Gulf Stream flexure. Towards Europe, the line bends southward, 

 and passes to the southwest cape of Portugal, Cape St. Vincent, or, 

 perhaps to the north cape of the Straits of Gibraltar. Vaillant, in the 

 Bonite, found the temperature at Cadiz in February, 49 §° to 56° F. 

 (9*7° to 13'4° C), which would indicate that Cadiz, although so far 

 south (and within sixty miles of Gibraltar), experiences at least as 

 low a mean temperature as 56° F. for a month or more of the winter 

 season. We have, however, drawn the line to Cape St. Vincent, which 

 is in nearly the same latitude. Between Toulon and Cadiz, the tem- 

 perature of the Mediterranean in February, according to Vaillant, was 

 55i° to 60£° F. (13-1° to 15'7° C), and it is probable, therefore, that 

 Gibraltar and the portion of the Mediterranean Sea east and north to 

 Marseilles, fall within the Temperate Region, between the isocrymes of 

 56° and 62° F., while the portion beyond Sardinia and the coast by 

 Algiers is in the Warm Temperate Region, between the isocrymes of 

 62° and 68° F. 



The line of 50° F., through the middle of the ocean, has the lati- 

 tude nearly of the southern cape at the entrance of the British Chan- 

 nel ; but approaching Europe it bends downward to the coast of 

 Portugal. The low temperature of 49£° observed by Vaillant at 

 Cadiz would carry it almost to this port, if this were the mean sea- 

 temperature of a month, instead of an extreme within the bay. The 

 line appears to terminate near latitude 42°, or six degrees north of the 

 isocryme of 56°. This allows for a diminution of a degree Fahrenheit 

 of temperature for a degree of latitude. A temperature as low as 61° 

 F. has been observed at several points within five degrees of this 

 coast in July, and a temperature of 52° F., in February. Vigo Bay, 

 just north of 42° north, lies with its entrance opening westward, well 

 calculated to receive the colder waters from the north; and at this 

 place, according to Mr. R. Mac Andrew,* who made several dredgings 

 with reference to the geographical distribution of species, the Mollusca 



* Rep. Brit. Assoc, 1850, p. 264. 



