TINY ROCK-BUILDERS. 145 



(3) Aporosa, very similar to the last, but 

 having their septa in multiples of six. 

 These did not appear till the Secon- 

 dary era, and are still abundant. 

 Sometimes madrepores are considered 

 as making up a fourth group called 

 Perforata. 



FlG. M.LitJiostrotion banaltiforme. 



These terms, however, now receive a different 

 interpretation. Professor Moseley thinks most of 

 the Tabulata are really Alcyonarians, and Professor 

 Nicholson says that some of the tabulate corals, 

 such as Millepora, have been shown to be Hydrozoa ; 

 others belong to Aporosa; others again, such as 

 Favosites and its allies, belong to Perforata; 

 others are referable to the Alcyonaria ; while 



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