260 COELENTERATA. 



existed in Europe during the earlier portions of the Cretaceous period. 

 In the earlier portion of the Tertiary period, again, vast coral-reefs were 

 formed in Central and Southern Europe, in Egypt, Syria, and Arabia, 

 and in parts of India. In the later portions of the Tertiary period, reefs 

 are much more sparingly developed in Europe, but they were at this time 

 formed on a large scale in the warmer regions of the earth's surface. In 

 Mesozoic, Kainozoic, and recent times alike, the chief genera of reef- 

 building corals belong to the families of the Astnzidcs, Poritidtz, and 

 Madreporidce, though the Oculinidce and Fimgidce also contribute to the 

 formation of reefs. 



With regard, finally, to the distribution in time of the Actinozoa^ 

 the Ctenophora, being devoid of hard parts, are unknown in the 

 fossil condition, and need no further consideration here. On the 

 other hand, the Zoantharia (including the Rugosd) and the Alcyon- 

 aria are very largely represented in past time, both sections of the 

 class being represented by extinct types in rocks as old as the Or- 

 dovician. Speaking generally, the Actinozoa of the Palaeozoic 

 period belong principally to the Rugose and Aporose divisions of 

 the Zoantharia and to certain abnormal groups of the Alcyonaria, 

 though the Perforate Zoantharia are by no means unrepresented in 

 rocks of this age. On the other hand, the Mesozoic and Kainozoic 

 periods are characterised by the predominance of the Perforate and 

 Aporose Zoantharians, these being the chief representatives of the 

 class at the present day. 



