212 



RUGOSA AND ALCYONARIA. 



spicuously quadripartite manner, except in a few cases ; 



tabula? are always present, and the interseptal loculi are more 

 or less broken up by the development of 

 dissepiments. The family is wholly Palae- 

 ozoic in its distribution, and it is divided 

 into the two great tribes of the Zaphren- 

 tince and CyathopJiyllince. 



In the Zaphrcntince, the corallum is 

 simple and free, conical, discoidal, or cylin- 

 drical in shape, with complete tabulae, and 

 usually few dissepiments. The septa are 

 Fi S .iw.-cyatka X onia rendered more or less irregular by the 



Daimam. A portion of presence of a septal fossula. In Zapli- 



wall of the theca is ' ' i n i i ni 



broken, in order to show TentlS itself, which IS the type of the 



SSS^*^^ g rou P> the corallum is turbinate (figs. 

 99 and 105), the tabulae pass from side 

 to side of the visceral chamber (fig. 98, c), and there is 

 a well-marked fossula, while the septa extend inwards to 

 near the centre of the coral. This large and important genus 

 is represented by numerous species in the Silurian, Devonian, 



Fig. 104. Petraia calicula. 

 Upper Silurian. 



Fig. I05.Zaphrentis StokesL 

 Upper Silurian. 



and Carboniferous rocks. The Silurian and Devonian genus 

 Petraia (fig. 104) has often been placed in the neighbour- 

 hood of Zaphrcntis, but there is considerable uncertainty as 



