210 RUGOSA AND ALCYONARIA. 



corallites of the compound corallum of the Rugosa are never 

 connected by a true ccenenchyma. Sometimes the corallites 

 are placed in close contact, so that the corallum becomes 

 " massive," and then they are usually united by a fusion of 

 their walls. Sometimes the walls are wanting, and the 

 corallites are united to one another by the extension and 

 confluence of their septa, as is seen in the genus Phillips- 

 astrcea (fig. 101), or the union may take place by the 



Fig. IQl.~-PhittipM8trcea Verneuilli. From the Devonian (Corniferous Limestone) 

 of N. America. 



development of lateral processes, very much as we have 

 seen in Syringopora. The production of compound coralla 

 is principally effected by lateral and calicular gemmation, 

 the latter process (see p. 186) being especially characteristic 

 of the Rugose Corals. 



The divisions of the Eugose Corals which were laid down 

 by Milne-Edwards and Haime, and which have subsequently 

 been generally adopted, are as follows : 



1. Stauridce. In this family the corallum may be simple 

 or compound, the septa are well developed, conspicuously 

 arranged in four systems, and both dissepiments and tabulae 

 are present. 



In Stauria (fig. 100, A), which is the type of the family, 

 there is a compound astreeiform corallum, four of the prin- 

 cipal septa forming a cross in each calice. The increase of 

 the corallum is effected by calicular gemmation, and there is 

 no columella. The genus is wholly Silurian in its range. 

 The genus Holocystis (fig. 102) is closely allied to Stauria, 

 but the corallites are united by their costse, and a styliform 

 columella is present. It is remarkable as being the sole 



