100 



Mr. J. D. Dana on Zoophytes. 



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 Caryophyllida, and probably 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 Geological Report 

 on Coral Reefs and Islands, will be particularly considered in the 

 forthcoming volume by the author. The cause referred to, is that 

 proceeding from original sites or centres of distribution. There is 

 sufficient evidence that such centres of distribution, as regards 

 zoophytes, are to be recognized. The species of corals in the 

 West Indies are in many respects peculiar, and not one can with 

 certainty be identified with any of the East Indies. The central 

 parts of the Pacific Ocean appear to be almost as peculiar in the 

 corals they afford ; but few from the Feejees have been found 

 to be identical with those of the Indian Ocean. A more com- 

 plete acquaintance with the corals of these different seas will 

 undoubtedly multiply the number of identical species ; but ob- 

 servations, thus far made, seem sufficient to establish as a fact, 

 that a large part of zoophytes are confined to a small longitudinal 

 range. This will be seen from the following table, exhibiting in 

 a general manner, as far as known, their geographical distri- 

 bution. Each column gives the number peculiar to the region 

 specified at top. 



* The Pocillopora, Sideroporce, Milleporee, Favosites, and other genera of 



Madreporacea, in which the cells are internally divided by horizontal septa. 



f Part of the Pontes of authors, the species having shallow cells closed 



