PERFORATA. 19*7 



and the septa are often well developed. There are no syn- 

 apticulse, and usually no dissepiments, but there may be 

 tabula?. The family makes its first undoubted appearance in 

 the Cretaceous (Actinacis), and is largely represented in the 

 Tertiaries, and by living forms in the " coral-reef region " of 

 the present era. 



The genus Madrepora itself, with its lobate, ramose, or 

 fasciculate corallum, and its loose and delicately echinulate 

 ccenenchyma, appears for the first time in the Eocene Ter- 

 tiary, and survives to the present day ; while the range of 

 the allied genus Astrceopora is essentially similar. 



3. Porit'idce. In this family the corallum is entirely 

 made up of reticulated calcareous tissue (" sclerenchyma "). 



Fig. 83. Alveopora spongiosa, one of the recent Poritidce (after Dana). A, Some of the 

 corallites cut vertically and enlarged, showing the tabulae and the perforated walls ; B, View 

 of the calices from above, enlarged. 



The septa are not lamellar, but are composed of styliform 

 processes, which constitute by their junction a sort of trellis- 

 work, and the walls are similarly constructed and are not 

 distinct from the ccenenchyma, when this is present. There 

 are a few dissepiments, but generally no tabulae. 



The oldest known types of the normal Poritidce appear in 

 the Silurian, where the family is represented by the curious 

 Protarcea and the nearly allied Stylaroea, both of which are 

 believed to be closely related to the Tertiary genus Litharcea. 

 In the Oolitic rocks we meet only with the singular genus 

 Microsolena (fig. 84), but in the Cretaceous we find Porites 

 itself. In the Tertiary rocks, again, the family is well re- 

 presented, principally by the still existing Porites, Alveo- 



