12 CORALS AND CORAL ISLANDS. 
P. gigantea V., several Astrangids, and a few other small 
species, besides a large variety under the Gorgonia tribe. At 
La Paz, on the California peninsula at the entrance to the Gulf, 
occur a small but beautiful Fungia (7. elegans V.), three Pori- 
tes, a Dendrophyllia, a Pocillipora, some Astrangids, and 
many fine Gorgonie. The character of the species is that. of 
the cooler torrid region, rather than that of the warmer 
torrid. 
Owing to the cold oceanic currents of the eastern border 
of the Pacific—one of which, that up the South American 
coast, is so strong and chilling as to push the southern isocryme 
of 68°, the coral-sea boundary, nearly to the Galapagos, 
and north of the equator—the coral-reef sea, just east of Pan- 
ama, is narrowed to 20°, which is 36° less of width than it has 
in mid ocean; and this suggests that these currents, by their 
temperature, as well as by their usual westward direction, have 
proved an obstacle to the transfer of mid-ocean species to the 
Panama coast. 
In the West Indies the reefs lie within the limits of the 
isocryme of 74° F., or the torrid region; and yet the variety 
of species and genera is very small compared with the same in 
the central Pacific. The region contains some large Madre- 
pores, the M. palmata, a spreading foliaceous species that 
forms clumps two yards in diameter; JL. cervicornis, a stout, 
sparsely-branched tree-like species, which attains a height of 
fifteen feet; JL prolifera, a handsome shrub-like species, of rathi- 
er crowded branches; besides others ; and these are marks of the 
existence of the warmer torrid region; yet the sea has not as 
high a temperature as the hottest part of the Pacific. The species 
of the Astraa tribe are few in number, and among the largest 
kinds are the Meandrine (the Diploria being here included). 
None of the free Fungide are known excepting the two spe- 
