98 CCELENTERATA. 



veloped, sclerodermic, with a true theca, and often presenting 

 both septa and tabulae combined. The septa are in multiples 

 of four (fig. 43), unlike the recent sclerodermic coralla, in which 

 they are in multiples of five or six. There is, further, no true 

 coenenchyma. Some of the Rugosa are simple; but others are 

 composite, increasing either by parietal or by calicular gemma- 

 tion. 

 The Palaeozoic corals (figs. 50-55), with hardly an exception, 



PALEOZOIC CORALS. 



Fig. y>.Syringcipora retifom 

 A Silurian Tabulate Coral. 



Fig. 51. Sytingopora verticillata. 

 Silurian. 



Fig. 52. Syringopora Dalmani. Fig. ^.Syringopora compacta. 



Silurian. Silurian. 



Fig. 54. Stromboties featagonus. 

 A Silurian Rugose Coral. 



Fig. 55. Strombodts gracilu. 

 Silurian. 



belong either to the Rugosa or to the Tabulate division of the 

 Zoantharia sclerodermata. The former are readily distinguish- 

 able from the latter in having well-developed septa, as a rule, 

 and in invariably having their septa in multiples of four. Until 



