66 



OUR COMMON BRITISH FOSSILS. 



belonging to the Rtigosa, such as Stromhodes^ Cya- 

 thophylbini (perhaps the most plentiful of them all), 

 Cyathaxinia (a simple coral), Lithostrotion^ Litho- 

 dendroji, etc. Perhaps the single coral which may 

 be regarded as the simplest in structure is Am- 



Fig. 49.— Recent Arborescent Perforate Coral {Oculina axillaris), 



plexus, and there is reason for believing that many- 

 more elaborate fossil corals pass through a kind of 

 Amplexus stage. 



A fourth division of corals is termed Perforata 

 (Fig. 49.) These are the familiar twig-like, branched 



