APOROSA. 191 



late Tertiaries, and Diplohelia is Eocene 'and Miocene. From 

 the researches of Verrill, it would appear that Pocillopora 

 (Miocene to Eecent), formerly referred to the Tabulata, should 

 be placed here, in which case we have a member of this 

 family exhibiting "tabulae" in a well -marked form, these 

 structures being occasionally present in Lophohelia also. 

 Probably the genus Seriatopora (which has been said to 

 occur even in the Palaeozoic rocks) should likewise be 

 referred to this family. On the other hand, the limits of 

 the group have been contracted in another direction by the 

 removal of Stylaster and allied genera to the Hydrozoa. 



4. Astrceidce. In this, the most important of all the 

 families of the Zoantharia sclerodermata, the corallum may 

 be simple or compound, usually increasing in the composite 



Fig. 77.- Columnar ia (?) Halli, showing the corallites partitioned off into storeys by 

 tabulae. Silurian. 



forms (fig. 73) by fission. There is no, or little, coenenchyma, 

 but an abundance of dissepiments, without synapticulae or 

 tabulae. 



Little is known of the distribution of Astrceidce in the 

 Palaeozoic period, but, as before said, Dr Martin Duncan, one 

 of the highest of authorities on this subject, regards the 

 Devonian Battersbyia and the Carboniferous Heterophyllia as 

 ancestral and aberrant types of the family (Palastrceidce). If 

 it were not, also, for the presence of tabulae, we should place 

 the Silurian genus Columnaria in this family, and as it is 

 now admitted that tabulae have little or no systematic sig- 

 nificance, it is difficult to see how this old form can be 



