126 



fotir families have nearly the same palseontological history, in 

 this, that they date their origin from the commencement of 

 the secondary epoch, and are represented in our present seas. 

 There is one important exception formed by the genus 

 Palceocyclus, one of the Fongid^ which belongs to the Silurian 

 period. The family Astreid^ dates from the Trias ; the 

 TuEBiNOLiD^ and Fungid^, with the exception enumerated, 

 date from the Lias, and the Octtlinid^ from the Great Oohte. 



2nd 8ub- Order. — The Zoanthakia peepoeata — have the 

 corallum composed essentially of porous sclerenchyma, the 

 septal apparatus is well developed, and consists of six primitive 

 elements. The plates are never imperforate, as in the preceding 

 sub-order Apokosa, but the septa are always porous, or even 

 reticulate. The visceral chamber is almost completely open 

 from top to bottom, and never filled up with dessepiments or 

 synapticulae, as in most of the Apoeosa, or with tabulae. This 

 sub-order includes two families — the Madeepoeid^, and the 



POEITID^. 



The first family, Madeepoeid^, characterises in a great 

 measure the Tertiary epoch and our modern seas ; one genus, 

 Discopsammia, is special to the Upper Chalk. 



The second family, Poeitid^, includes the Silurian genus, 

 Protaroea, the Devonian genus, Pleurodyctium, forir Jurassic, and 

 several tertiary and existing genera. 



From this analysis it appears that these two sub-orders, 

 ZoANTHAEiA APOEOSA and ZoANTHAEiA PEEFOEATA, hved in the 

 Silurian period, and have continued to flourish throughout all 

 the subsequent epochs. They are rare in the Palaeozoic, more 

 numerous in the Mesozoic, and attain their fall development in 

 the Tertiary epoch, and in the seas of the present time, forming 

 the reef-builders of many Coral formations in the Indo-Pacific. 



Srd Sub-Order. — Zoanthaeia tabulata — ^have the corallum 

 composed of a well-developed mural system, with the septa 

 rudimentary or absent. The visceral chambers are divided into 

 a series of stories by complete transverse tabulae or diaphragms ; 

 these floors differ from those of the AsTEEiDiE in being 

 independent of the septa, and forming as many complete 



