234 STALK-EYED CRUSTACEA. 
of Mexico, and that this connection was not completely severed till late in 
the Tertiary period. It is obvious that the former uninterrupted sweep of 
the equatorial current from the Atlantic into the Pacific must have served as 
an important agent in disseminating tropical types around the earth. 
Littoral species of the cold and temperate zones have this advantage over 
tropical types in the matter of distribution on north and south lines: the 
temperature of the sea rapidly falls in passing from the surface downward, 
so that even under the equator a temperate degree of heat is found at a mod- 
erate depth. Availing themselves of this, many littoral species of the North 
and South Temperate realms, by moving into the deeper and colder waters 
have extended their range toward the equator. For example, Cancer borealis, 
whose normal range as a strictly shore species is limited on the south by the 
New England coast, was found during one of the cruises of the “ Blake” in 142 
fathoms off the coast of South Carolina, living in a temperature of 563 F. 
under a surface temperature of 81°. Eluding in this way the fatal heat of 
the tropics, certain species of the temperate zone have actually passed under 
the equator and invaded the opposite hemisphere. Cancer longipes, a shore 
5) 
crab of Chile, was dredged by the “ Albatross” in the Gulf of Panama ata 
depth of 210-286 fathoms, above the seventh parallel of north latitude. The 
bottom temperature here was 46° to 49° F., while the surface temperature 
was 72°-74°. The extreme surface temperatures at Valparaiso are given as 
52° and 62°.* Platymera gaudichaudii is another crab long known to nat- 
uralists as a native of the shores near Valparaiso. This species also was found 
by the “ Albatross” in the Gulf of Panama, living at a depth of 127 fathoms 
in a temperature of 56° (surface temperature, 74°). The same species was 
” 
secured during another cruise of the “ Albatross”? much further north, off 
the California coast from the latitude of San Diego to San Francisco. It is 
of interest to note that near the northern limit it was found even at as slight 
a depth as 26 fathoms, where it enjoyed the congenial temperature of 58°. 
In this way, doubtless, it has come about that many littoral genera 
(e. g. Cancer and Lithodes) of the Arctic and North Temperate regions are 
represented on the shores of corresponding latitudes in the southern hemi- 
sphere, albeit they are unknown from the vast stretch of intervening coast. 
This extension of the range of Arctic and Temperate littoral animals 
toward the equator in the cold off-shore waters finds a close parallel in the 
distribution of land animals. I refer to the well known influence which alti- 
* The means of the coldest and warmest thirty consecutive days of the year. 
—_ 
—s 
