the Geographical Distribution of Marine Species. 159 
Gulf Stream, which here (after a previous east and west course, 
occasioned by the Newfoundland 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 sea-temperature at Cadiz in February, 493° to 56° F. (9°79 
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 temperature of the Mediterranean in February, ac- 
cording to Vaillant, was 554° to 604° EF. (13°19 to 15-79 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 
annel; but approaching Europe it bends downward to the 
coast of Portugal. The low temperature of 494° 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 with- 
in 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 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, ac- 
cording to Mr. R. Mac Andrew, who made several dredgings 
with reference to the geographical distribution 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 @ 
natural boundary between the south and the north. The cold 
waters from the north and the ice of Newfoundland Banks, pr 
the line close upon those of 50° and 56° F. But after getting 
beyond these influences, it rapidly rises to the north, owing to the 
* Rep. Brit. Assoc, 1850,p.264 
