MADREPORARIA PERFORATA. 3 I I 



genera, such as Lithar&a, Rhodara>a, &c. We may also place here the 

 ancient genera Stylarcea and Protara'a, both of which commence in the 

 Ordovician rocks, the latter surviving into the Devonian period. In the 

 Devonian rocks we find, further, the singular genus Clezstopora, repre- 

 sented only by the little C. gcometrica of the European Devonian rocks, 

 in which the corallum (fig. 192, a) is composed of short polygonal coral- 

 lites, forming a discoid colony which is usually attached by its under 

 surface to some foreign body. The corallites are united by fusion of 

 their walls, which are slightly porous, and the septa are only present as 

 marginal striae (fig. 192, B). The characteristic feature about the genus, 

 however, is that the whole of the visceral chamber, below the calice, 

 is filled with reticulated or trabecular calcareous tissue (fig. 192, c 

 and D). 



Lastly, a third group of the Poritidce is typified by the genus Alveopora, 

 the most characteristic feature of the group being that the walls of the 

 corallites (fig. 193, a) are spongy and porous, while the septa (fig. 193, b) 

 are trabecular, and well-developed tabulae are usually present. The 















anl 





i7^n| 





HEfti 









lp! 



C f i 



III 



pl£§B ||| 





BljH| 





mm 







Fig. 193.— Alveopora spongiosa, one of the recent Poritidce (after Dana). A, Some ox the 

 corallites cut vertically and enlarged, showing the tabula? and the perforated walls; b, View of 

 the calices from above, enlarged. 



genus Alveopora itself ranges from the Eocene Tertiary to the present 

 day, but the genus Arceopora, properly referred here by Waagen, is 

 found in the Devonian deposits of Australia and the Carboniferous rocks 

 of India. In this ancient type the corallum is massive, and is composed 

 of polygonal corallites, which have their walls fused with one another. 

 The walls are composed of spongy tissue, with irregular pores, the septa 

 being trabecular or reticulate, while tabulae may be more or less exten- 

 sively developed. The Cretaceous genus Ko?iinckia, though incompletely 

 investigated, may also be placed here as a provisional arrangement ; 

 while the recent genus Favositipora, as described by Mr Saville Kent, 

 would appear to form a connecting link between Alveopora and Fa- 

 vosites. 



Family 4. Favositidtz. — This large and important family of Corals 

 is characterised by the possession of a variably shaped corallum 

 composed of polygonal or sub - cylindrical corallites, which are 

 usually in close contact throughout their entire extent, but are not 

 completely united by fusion of their walls. The walls of the 

 corallites are porous, the visceral chambers of adjacent corallites 



