Mr Dana on the Geographical Distribution of Zoophytes. 43 



nas, Madrepores, &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 spe- 

 cies. At the Sandwich Islands, which are near the northern 

 limits of the coral seas, Porites and Pocilloporse prevail, and 

 there are very few species of the genera Astray, Mussa,* and 

 Meandrina, which are common nearer the equator. 



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

 larly small. Twenty, or perhaps sixteen^ fathoms will include 

 very nearly all the species of the Madrepore and Astraea 

 tribes. t Temperature has little or no influence in occasion- 

 ing this limit, as 68° F. will not be found under the equator 

 short of a depth of 100 fathoms. Light and pressure — the 

 latter aifccting the amount of air for aeration, are probably 

 the principal causes. The waves, moreover, cannot aid in 

 renewing the expended air below, as they do at the surface. 



In recapitulation, we state, that the Astraeacea, Madrepo- 

 racea and the Gemmiporidae among the Caryophyllacea, are, 

 with few exceptions, confined to the coral-reef seas,| and to 

 within 20 fathoms of the surface. The Caryophyllid9e§ ex- 

 tend from the equator to the frigid zone, and some species 

 occur at a depth of 200 fathoms or more. The Alcyonaria 

 have an equally wide range with the Caryophyllidas, and pro- 

 bably reach still farther towards the poles. The Hydroidea 

 range from the equator to the polar regions, but are most 

 abundant in the waters of the temperate zone. 



Besides the above mentioned limiting causes, there are 

 others of importance, one of which may be alluded to in this 

 place ; the remaining, belonging more properly to the Geolo- 

 gical Report on Coral Reefs and Islands, will be particularly 

 considered in the forthcoming volume by the author. The 



* Lobophyllia of Blainville, Mussa of Oken. 



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

 Islands. 



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

 genus Flabollum, some Turbinalioe, and the Lobophyllia, having entire loniella;. 



§ The CanjophijllUo of Blainville, with the Doidrophijllia', OcuUna', &c. 



