ACTINOZOA. MADREPORARIA. 55 



buds spring from branches or stolons, which are given off 

 from the base of the corallite. Fission commences by 

 the mouth becoming slightly constricted, this goes on 

 until two mouths and two polyps are formed ; and this 

 division is of course repeated in the skeleton. When in 

 a compound form, the individual corallites are free from 

 one another, the corallum is termed dendroid (fig. 12 A] ; 

 when they are in contact, it is massive. Sometimes the 

 spaces between the individual corallites are filled up with 

 calcareous material formed by the coenosarc, and known as 

 the casnenchyma. 



The Madreporaria 1 are divided into four sections (1) 

 Aporosa, (2) Rugosa, (3) Fungida, (4) Perforata. 



Section /. Aporosa. 



The theca and septa are not perforated but solid. 

 Dissepiments, and sometimes also tabulae and synapticulse, 

 are present. The septa are generally in multiples of six. 



Montlivaltia. Corallum simple, fixed or free; tur- 

 binate, cylindrical, or discoidal. Epitheca well developed, 

 theca feeble. Columella absent. Septa numerous, strong 

 and dentate, often exsert. Dissepiments abundant. In 

 England, Lias to Corallian; foreign, Trias to Recent. 



Isastraea. Compound, massive ; calyces polygonal. 

 Walls of the corallites fused along their entire length. 

 Columella rudimentary or absent. Septa thin and close 



1 Until recently one of the divisions of the Madreporaria was the 

 Tabulata. This was characterised by the well-developed tabulae, and the 

 rudimentary septa ; but it is now considered to be an artificial group and 

 its genera are placed in the Aporosa, Perforata, and Alcyonaria. It 

 included amongst others the following, Heliolites, Favosites, Syringopora, 

 and Halysites. 



