306 



ZOANTHARIA. 



Section IV. Madreporaria Perforata. 



This section includes simple or composite Madreporarians in 

 which the calcareous tissue (sclerenchyma) of the corallum is more 

 or less conspicuously porous or reticulate (fig. 187, c) ; the visceral 

 chambers of the corallites being thus placed, in the compound 

 forms, in communication with one another. The septa may be 

 solid, but are usually more or less porous, being often represented 

 by irregular trabecular, or, in other cases, by rows of calcareous 

 spines. Dissepiments are usually present, and tabulae are com- 

 monly developed. The existing Madreporaria Perforata fall into 

 the three groups of the En' sammidce, Madreporidce, and Poritidce, 

 while we may place here the three extinct groups of the Favositidce, 

 Syringopo?-idce, and Thecidce. These three last-mentioned groups 



Fig. 187. — a, Dendrophyllia clegans, trom the Oligocene Tertiary of Brockenhurst, of the nat- 

 ural size ; b, Transverse section of the same, enlarged (after Zittel) ; ,c, Portion of a section of a 

 recent species of Dendrophyllia, showing the porous structure of the skeleton. 



are essentially Palaeozoic, the Favositidce. alone having any Mesozoic 

 representative (the Koninckia of the Cretaceous rocks). Of the 

 three existing groups of the Perforata, the Poritidce appear to be 

 the most ancient, the Ordovician genus Protaraza belonging to this 

 family, while the Calapoecia (Co/umnopora) of the same formation 

 links the Poritidce with the Favositidce. The Devonian genera 

 Arceopora and Cleistopora, and the Carboniferous genus Palceacis 

 (fig. 188) may also be referred to the Poritidce. The Eupsa7nmidce 

 are also an ancient group, being represented in the Silurian rocks 

 by the genus Calostylis. On the other hand, the Madreporidce are 

 of comparatively modern origin, the first known types appearing in 

 the Tertiary deposits. Upon the whole, however, the existing groups 

 of the Eupsammidce, Poritidce, and Madreporidce do not present 



