illustrating the Distribution of Marine Animals. 197 



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 temperatures 

 of the Mediterranean in February, according to Vaillant, 

 was 55J° to 60i° F. (134° 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 

 latitude nearly of the southern cape at the entrance of the 

 British Channel ; but approaching Europe it bends down- 

 ward 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 tem- 

 perature as low as 61° F. has been observed at several 

 points within five degrees of this coast in July, and a tem- 

 perature 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. MacAndrew, who made 

 several dredgings with reference to the geographical distri- 

 bution of species, the Mollusca have the character rather of 

 those of the British Channel than of the Mediterranean.* 



Isocryme of 44° F. — This line commences on the west, at 

 Cape Cod, where there is a remarkable transition in species, 

 and a natural boundary between the south and the north. 

 The cold waters from the north, and the ice of Newfoundland 

 Banks, press the line close upon those of 50° and 56° F. 

 But after getting beyond these influences, it rapidly rises to 



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



