62 



OUR COMMON BRITISH FOSSILS. 



(whose specific name comes from the bright blue 

 colour of the stony structure, which in other modern 

 corals is usually white) is an Alcyonarian, more 

 nearly related to some sea-fans than to true corals, 

 It is plentiful in equatorial seas, and especially off the 

 Bermudas. It has not indistinct traces of septa. The 

 genus of fossil corals called Heliolites, abundant in 



Fig. 41. " Chain-Coral " (Halysites catenulatus), as usually found intact in 

 round masses. 



the Silurian and Devonian limestones, does not differ 

 in any important particular from the living Heliopora, 

 and, like it, no doubt belonged to the Alcyonaria. 



The division of fossil corals called Rtigosa, on the 

 other hand, is distinguished by well-marked septa, 

 radiating from the coral walls towards the centre, in 

 the pretty star-shaped fashion which caused Cuvier to 



