Mr. J. D. Dana on Zoophytes. 99 



region included mostly between the parallels of 28° north and 

 south of the equator, — while the Caryophyllia family are spread 

 as widely as the species of Actinia. Several species of Caryo- 

 phyllidce occur in the Mediterranean, and others in the high 

 northern seas, and they are met with at depths of several hundred 

 feet. They are also common among the coral reefs of the tropics. 



The Madreporacea and Astreeacea, with the Gemmiporidce, are 

 the principal constituents of coral reefs. The temperature limit- 

 ing their geographical range is 66° or 68° F., this being the 

 winter temperature of the ocean on the outskirts of the reef- 

 growing seas. The waters may sometimes sink to 64°, but this 

 appears to be a temperature which they can endure, and not that 

 in which they germinate. The extremes which they will survive 

 prove only their powers of endurance, and do not affect the above 

 statement ; for their geographical distribution will be determined 

 by the temperature which limits their powers of germination. 



The temperature of the ocean in the warmest parts of the Pa- 

 cific varies from 80° to 85°, and here Astrseas, Meandrinas, Ma- 

 drepores, &c. are developed with peculiar luxuriance, along with 

 thousands of other strange and beautiful forms of tropical life. A 

 range from the above temperature to 72° does not appear to be 

 too great for the most fastidious species. At the Sandwich Islands, 

 which are near the northern limits of the coral seas, Porites and 

 Pocilloporce prevail, and there are very few species of the genera 

 Astrcea, Mussa* and Meandrina, which are common nearer the 

 equator. 



The range of these reef-forming corals in depth is singularly 

 small. Twenty or perhaps sixteen fathoms will include very 

 nearly all the species of the Madrepore and Astrsea tribes j\ Tem- 

 perature has little or no influence in occasioning this limit, as 

 68° F. will not be found under the equator short of a depth of 

 100 fathoms. Light and pressure, the latter affecting the amount 

 of air for aeration, are probably the principal causes. The waves, 

 moreover, seldom reaching to a greater depth than thirty fathoms, 

 cannot aid in renewing the expended air below as they do at the 

 surface. 



In recapitulation we state that the Astrseacea, Madreporacea, 

 and the Gemmiporidse among the Caryophyllacea, are, with few 

 exceptions, confined to the coral-reef seas J, and to within twenty 

 fathoms of the surface. The Caryophyllidce^ extend from the 



* Lobophyllia of Blainville, Mussa of Oken. 



t The evidences on this point will be presented in the Report on Coral 

 Islands. 



X The exceptions belong mostly to the genus Euphyllia, which includes 

 the genus Flabellum, some TurbinalicE and the Lobophyllia, having entire 

 lamellae. 



§ The Caryophyllia of Blainville, with the Dendrophyllite, Oculina, &c. 



