ACTINOZOA. ' 235 



Alcyonaria and Ctenophoray of which one genus, 

 Mertensia, is said to be exclusively arctic, chiefly 

 represent the class. The Pennatulidce appear 

 more numerous than other Alcyonaria around 

 the northern colder temperate shores, seven spe- 

 cies being named in the Norwegian fauna of Sars, 

 while but three have yet been recorded as British. 

 UTYibellularia, a very aberrant member of this 

 family, which presents a rod-like coenosarc six feet 

 in length, crowned with a spreading tuft of polypes 

 at its summit, is only known from the published 

 descriptions of two specimens, dredged from a 

 depth of 236 fathoms, off the coast of Grreenland, 

 about the middle of the last century. 



Among genera of Actinozoa which enjoy a 

 wide distribution. Actinia, Alcyonium, Zoanthus, 

 and Gorgonia are perhaps best worthy of men- 

 tion. To this list should be added the names of 

 several forms of Ctenophorct, than which few ma- 

 rine animals appeared so well adapted to thrive 

 under every variety of climatal conditions. Two 

 genera in particular, Beroe and Pleurobrachia, 

 are remarkable for their unbounded geographical 

 area. 



With less confidence can the names of such 

 Actinozoa as are restricted in their range be, at 

 present, insisted on. Eenewed observations show 

 that the number of extra-tropical genera, once 

 thought to be peculiar to certain regions, must 

 undergo considerable diminution. Of specific 

 forms, however, not a few seem to characterise the 

 various seas and shores to which they are confined. 



The existence of natural barriers, whether of 

 land or deep water, exercises a marked influence 

 on the distribution of the Actinozoa, The differ- 



