264 ZOANTHARIA. 



polypes united with one another directly, or connected by a general 

 coenosarc. 



A strictly natural classification of the Madreporaria has still to be 

 framed. By Milne-Edwards and Haime they were divided into the 

 four sections of the Aporosa, Perforata, Tabulata, and Tubulosa ; 

 while these authorities considered the Rugosa as a distinct order. 

 The section of the Tabulata (" Tabulate Corals ") has, however, 

 been shown to be a miscellaneous and artificial assemblage, and the 

 types formerly included in it have now found a place in the Aporose 

 or Perforate sections of the order, or have been relegated to the 

 Alcyonaria. The section of the Tubulosa, again, is a small and 

 imperfectly understood one, and the forms included in it may be 

 temporarily placed in the Alcyonaria. Lastly, recent researches and 

 discoveries have rendered hardly tenable the retention of the Rugosa 

 as a separate order of Actinozoa ; though the true affinities of many 

 of the so-called Rugose Corals are still very uncertain. In the present 

 state of our knowledge, the Madreporai'ia may be divided into the 

 four primary sections of the Aporosa, Rugosa, Fungida, and Per- 

 forata. Of these, the Fungida do not appear to have come into 

 existence prior to the Jurassic period ; but the remaining three sec- 

 tions were differentiated as early as the Ordovician period. 



Section I. Madreporaria Aporosa. 



The division of the Aporosa comprises those Madreporarians in 

 which the corallum is composed of more or less compact and solid 

 sclerenchyma, the " theca " or wall surrounding the visceral chamber 

 being complete, and not perforated by apertures or pores (fig. 140). 

 An " epitheca " may be present. The septa are well developed, and 

 usually have the form of solid lamellae, though they are in some 

 cases more or less cribriform. The interseptal loculi may be open 

 throughout, but endothecal tissue in the form of " dissepiments " is 

 usually more or less largely developed, while " synapticula " and 

 " tabulae " are sometimes present. The corallum may be simple or 

 composite. The symmetry may be completely radial (Mussa and 

 Euphyllia), or bilateral. The arrangement of the septa is typically 

 hexameral, but may be tetrameral, pentameral, or otherwise abnormal. 



It is difficult to speak positively as to the geological distribution of 

 the Madreporaria Aporosa, owing to the uncertainty which attaches 

 to the precise affinities of many fossil Corals. There are, however, 

 various Palaeozoic types which may most suitably find a place here, 

 the Ordovician genus Colum?iaria (Favistella) being apparently the 

 most ancient of these. The Silurian genus Stauria, in spite of its 

 tetrameral symmetry, may likewise be regarded as an Astraeid ; while 

 Dmicanella and Cyathaxonia, the former Silurian and the latter Car- 



