214 



RUGOSA AND ALCYONARIA. 



In Cyathopliyllum, the type- genus of the family, the coral- 

 lum may be simple or compound, and the septa are well 



developed, some of them extend- 

 ing to the centre of the visceral 

 chamber, where they are twisted 

 together to form a spurious colu- 

 niella (fig. 106, B). The genus 

 ranges from the Silurian to the 

 Carboniferous. In Heliophyllum 

 (figs. 106, A, and 107) the septa 

 are provided with singular dissepi- 

 mental outgrowths, which appear 

 as so many spines or teeth on the 

 free edges of the septa within 



Fig. 107. A young form of Helio- r 



phyttum Halli, viewed from one side. the CallCC, aild which glV6 them 



' a characteristically cross -barred 



appearance in transverse sections. 



The genus is abundantly represented in the Devonian. 

 Palceocyclns, which is exclusively Silurian, may be placed 

 here in the meanwhile, though it is typically discoid in 

 form, and has other peculiarities as well. The Silurian 

 genus Omphyma is closely related to the simple forms of 

 Cyathophyllum,. but the septa are divided into four groups 

 by as many shallow depressions or fossulaa, and the coral- 



Fig. 108. Strombodes pentagonus. 

 A Silurian Rugose Coral. 



Fig. 109. Strombodes gracilis. 

 Silurian. 



lum is attached by root-like prolongations of the epitheca. 

 In the genus Acervularia, again, of the Silurian and Devonian, 

 we have forms in many respects resembling the compound 

 species of Cyathophyllwn, but differing in the fact that each 



