42 Mr Dana on the Geographical Distribution of Zoophytes. 



implant themselves upon the dead zoophyte, forming a mossy 

 covering, taking the place of the faded coral blossom. 



The species are most abundant, however, in the waters o 

 the temperate zone, and are common upon some portions of 

 our own coast. 



Order Actinoidea. — The Actinoidea are marine zoophytes. 

 All oceans have their species, yet in the torrid zone they 

 more especially abound, and display most variedly their co- 

 lours and singular forms. 



The soft Actinidae and the Alcyonaria have the widest 

 range, occurring both among the coral reefs of the equato- 

 rial regions, and to the north and south beyond the temperate 

 zone. The Mediterranean affords species of Gorgonia, Co- 

 mllium, and Alcyonium, besides numerous Actinoidea. The 

 coasts of Britain have also their Alcyonia and Actinia ; and 

 from far in the northern seas come the Umbellularia, and 

 some other species of the Pennatula family. 



Among the coral-making Actiniaria, the Madrepore and As- 

 traea tribes are almost exclusively confined to the coral-reef 

 seas, a region included mostly between the parallels of 28° 

 north and south of the equator, while the Caryophyllia fa- 

 mily are spread as widely as the species of Actinia. Seve- 

 ral species of Caryophyllida3 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 Astrseacea, with the Gemmiporicla?, 

 are the principal constituents of coral reefs. The tempera- 

 ture limiting their geographical range is QQ° 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 endur- 

 ance, and do not affect the above statement ; for their geo- 

 graphical distribution will be determined by the temperature 

 which limits their powers of germination. 



The temperature of the ocean in the warmest parts of the 

 Pacific varies from 80'' to 85°, and here Astrseas, Meandri- 



