the Geographical Distribution of Marine Species. 321 
We thence deduce, that the mean position of the isocryme of 
74° EF’, is along the parallel of 20°, this being the average between 
the means for the North and South Pacific. In the same manner 
we infer that the mean position of the isocryme of 68° F. is 
along the parallel of 27°. 
The southern isocrymes of 56° and 62° F., are evidently 
thrown into abnormal proximity by the cold waters of the south. 
This current flows eastward over the position of the isocryme of 
4° F., and consequently in that latitude has nearly this tempera- 
ture, although colder to the south. Hence it produces little effect 
in deflecting the line of 44° F’.; moreover, the line of 50° F. is not 
pushed upward by it. But the lines of 56° and 62° F.. are thrown 
considerably to the north by its influence, and the Warm Tem- 
perate and Temperate Regions are made very narrow. With 
these facts in view, we judge from a comparison of the North and 
South Pacific lines, that the mean position for the isocryme of 
62° FE. is the parallel of 32°; and for 56° F., the parallel of 37° ; 
for the isocryme of 50° F., the mean position is nearly the paral- 
lel of 42°; for 44° F., the parallel of 47°; for 35° F., the paral- 
lel of 56°. There is thus a mean difference of five degrees of 
latitude for six degrees of Fahrenheit, excepting near the equator 
and between 35° and 44° F. These results may be tabulated 
as follows. 
[socryme of 80° F.,_ _.. ‘ Parallel of 6° 
66 e) : : “ 20° 
“ 68°, i, Be 
“ 62°, os 10% Soe BOP 
“ 56°, Fagl . hs neg ER 
« 50°, ee “  4g0 
«“ 44°, Prt: “ 47° 
3°, ‘ : 
Using these results as a key for comparison we at once perceive 
the great influence of the oceanic movements on climate and on 
the geographical distribution of marine life. 
i Atlantic has 
e polar or extra-tropical current of the Southern 
a more northward course in mid-ocean than that of the Pacific. 
* We may hence deduce the temperature of those isocrymes to which the a 
of latitude for every five degrees would normally correspond. They woul be or 
20°: 74° F,- for 25°, 70° F.; for 80°, 64-49 F.; for 35°, 58°4° F.; for 40°, 524° F.; 
for 45°, 46-4° F.: for 50°, 41° F.; for 55°, 36° F.; for 60°, 31° F. 
Srconp Series, Vol. XVI, No. 48.—Noy. 1853. 
