106 



Guide to the Invertelrata. 



Corals. They belong to the group of Rugosa, or corals arranged on a 

 GALLEEY quadriradial type, the principal septa being four in number. 



X. 

 West Side. 



Wall- 

 cases 16, 

 Table- 

 case 7. 



Fig. 160. — The "chain-coral," Halysites catenularia, Linn. Wenlock Limestone 

 (Upper Silurian) : Dudley. 



This group was at one time regarded as distinct from the Hexa- 

 coralla and Octocoralla, and has even been included among the 

 Hydiozoa; but it has now been dispersed, some genera, such as 

 Ilalysiteit, being probably Alcyojiaria, and the rest distributed 

 among the Zoantharia. The most interesting Silurian forms 



Fio. \&\.—Omphyma subturbimiia, D'Orb, Wenlock Limestone: Dudley. 

 (Prestwich's Geology.) 



are the simple pyramidal Goniophyllum,, discoid PalceocycluSy 

 and conical Omphyma (Fig. 161); the massive Stromhodes and 

 Acervularia; and Cyathophyllum, with its peculiar method of 



