PERFORATA. 195 



resembling the latter in having no synapticulai, and in pos- 

 sessing dissepiments. The only genus of this family is 

 Merulina, and it is not known to possess any fossil repre- 

 sentatives. 



II. PERFORATA. 



In the Perforate section of the Zoantharia sclerodermata, 

 the calcareous tissue of the corallum is more or less porous, 

 often spongy or reticulate, the " wall " of corallites being always 

 perforated by more or fewer apertures. The septa may be 

 well developed, but they are usually more or less porous, and 

 are sometimes represented by mere calcareous trabeculse. There 

 may be imperfect dissepiments, and sometimes there are well- 

 developed tabulae, but in general the visceral chamber is open 

 from top to bottom, the interseptal loculi being continuous. 



Taken as a whole, the Perforate Corals must be regarded 

 as an essentially Tertiary and Recent group. The only 

 Palaeozoic Corals which can at present be referred to the Per- 

 forata, with anything like certainty, are the Protarcea of the 

 Lower Silurian, and the Calostylis of the upper division of the 

 same formation. The Lower Silurian genus Columnopora 

 may possibly be one of the Poritidce, and there is con- 

 siderable probability that the true place of the great and 

 important family of Palseozoic Corals termed the Favositidce 

 is truly in this section, but we shall provisionally consider 

 these among the Tabulata. In deposits later than the 

 Silurian, the only forms which have been referred here 

 namely, Plcurodictyum and Palceacis are certainly wrongly 

 placed, the former being founded upon casts of a member of 

 the Favositidce, while the latter is probably a sponge, and 

 is apparently not a coral. In the Permian rocks, the 

 Trias, and the Lias, no Perforate Corals are known ; and in 

 the Oolitic series we have only the aberrant genus Microsolena 

 (including Dendrarcea), an ancient type of the Poritidce. 

 In the Cretaceous series, however, we have examples of all 

 the existing families of this section, and in the Tertiary 

 period we find a great development of Perforate Corals, the 

 group apparently reaching its maximum at the present day. 



