394 COELENTERATA ANTHOZOA chap. 



Cyathophyllidae, a family of solitary and colonial corals with 

 numerous radially arranged septa, extending from the Silurian to 

 the Carboniferous limestone. It includes the genera Cyatho- 

 pliyllum, which was very abundant in Devonian times, and 

 Litliostrotion, which, in the times of the formation of the 

 Carboniferous limestone, occurred in continuous masses extending 

 over great areas of the sea-bottom. The Cyathophyllidae may 

 possibly be ancestral to the representatives of both Astraeidae 

 and Fungiidae, which appeared in the Triassic strata. 



The Cyathaxoniidae form a family of solitary turbinate or 

 horn-shaped corals, with septa showing a regular, radial arrange- 

 ment, and may have been the ancestors of the modern family 

 Turbinoliidae. They have the same geological range as the 

 Cyathophyllidae. 



The Cystiphyllidae. — This family consists of solitary corals 

 with very thin septa ; the interseptal spaces are filled with 

 an abundant vesicular substance called the " stereoplasm." The 

 systematic position of this family is very doubtful, as the 

 structure is evidently much destroyed, but by some authors it is 

 supposed to be ancestral to the family Eupsammiidae. 



These three families, together with the Zaphrentidae (p. 406), 

 were formerly grouped together as the Tetracoralla or Eugosa. 



Sub-Order 1. Entocnemaria. 



Madreporaria forming perforate coralla, with calices that do 

 not project above, or project only slightly above the surface of the 

 coenosare. The zooids of each colony are usually small and 

 crowded. The mesenteries arise in bilateral pairs, and the 

 increase in their number takes place in the chamber between the 

 ventral or the dorsal pairs of directives. The corals included in 

 this order are among the most important of the reef-builders. 

 On many of the recent coral reefs they occur in enormous 

 numbers and of great individual size. But although so prevalent 

 upon recent reefs, they appear to have played a far less important 

 part in the formation of the reefs of the early Tertiary times, and 

 in the reefs of times antecedent to the Tertiary they were rare or 

 absent. 



Judging from the structure of the skeleton and the palaeonto- 

 logical history alone it might be thought that the .Entocnemaria 



