3io 



ZOANTHARIA. 



and is mainly Mesozoic and Tertiary, numerous forms existing at 

 the present day. 



The group of the Poritidcz which is most nearly allied to the Mad- 

 reporidce is that of which Turbi?iaria is the type, characterised by 

 the fact that the corallites have distinct walls and are united by an 

 abundant reticulate or spongy ccenenchyma. Turbinaria itself ranges 

 from the Miocene Tertiary to the present day, and allied types are 

 Actinacis (Cretaceous to Oligocene) and Astrceopora (Eocene to Recent). 

 More or less closely allied to the preceding are the little Carboniferous 

 corals which constitute the genus Palczacis. 1 In this genus the corallum 

 (fig. 188) is composed of short and wide corallites, united together directly 

 or by the intervention of a limited amount of ccenenchyma. The tissue 

 of the skeleton is more or less trabecular (fig. 188, b), and the septa are 

 obsolete, being represented only by rows of granules in the interior of the 

 deep calices. The species of Palozacis are found growing upon the stems 

 of Crinoids and other foreign bodies in the Lower Carboniferous rocks 

 of both Europe and North America. 



The genus Porites is the type of another group of the Poritidcz, char- 

 acterised by the reticulated sclerenchyma, the almost total or total absence 

 of a ccenenchyma, and the generally trabecular septa. The species of 



Fig. 192. — Cleistofiora geometrica, Edw. & Haime, sp. a, Upper surface of a full-sized 

 individual, of the natural size; b, A single calice enlarged; c, Vertical section of a specimen 

 growing upon a Brachiopod, enlarged five times ; d, Tangential section of the same specimen 

 similarly enlarged. (Original.) 



Porites are abundant at the present day, and are largely concerned 

 with the building up of coral-reefs ; while the earliest types of the genus 

 occur in the Cretaceous rocks. Allied to Porites are various Tertiary 



1 Misled by certain peculiarities in the minute structure of the skeleton, the 

 present writer was formerly induced to believe that Palceacis did not properly 

 belong to the corals. 



