112 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 (F. elegansY.), three Pon- 

 tes, a Dendrophyllia, a Pocillipora, some Astrangids, and 

 many fine Gorgoniae. 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, even beyond 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. jpalmata, a spreading foliaceous species that 

 forms clumps two yards in diameter ; M. cervicornis, a stout, 

 sparsely-branched tree-like species, which attains a height of 

 fifteen feet; M. prolifera, a handsome shrub-like species, of rath- 

 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 Astrsea tribe are few in number, and among the largest 

 kinds are the Mseandrinse (the Diploria being here included). 

 None of the free Fungidae are known excepting the two spe- 



