SUBCLASS II HEXACORALLA 93 



common coenenchyma. Endothecal structures are frequently present in tlie 

 form of synapticulae, dissepiments, and tabulae. 



The order of stone corals or Madreporaria {Zoantharia sderodermata) was 

 divided by Milne Edwards and Haime into five suborders : Eugosa, Tabulata, 

 Tuh'ulosa, Perforata, and Aporosa. Of these, the Rugosa have been elevated by 

 Haeckel into a separate subclass under the name of Tetracoralla. The groups 

 Aporosa and Perforata are called Hexacoralla ; while the affinities of the 



Fig. 129. 



Diagram showing the order of appearance of all the mesenteries in a polyp having three cycles. The Roman 

 numerals represent the cycles to which the mesenteries belong, and the smaller Arabic numerals indicate the 

 order in which the mesentery appeared within its cycle. The regularity here indicated is constant for the 

 primary and secondary cycles, but departure may be encountered in the third cycle (after Duerden). 



Tabulata (with which the Tuhulosa are now generally included) are still 

 unsatisfactorily determined. The group is certainly composed of a varied 

 assemblage of forms, some of which have been assigned to the Hexacoralla, 

 some to the Odocoralla, and some to the Hydrozoa and Bryozoa. 



Order 1. MADREPORARIA Milne Edwards. ^ 



(Zoantharia sderodermata E. and H.) 



Radially symmetrical sclerodermous corals with typically hexameral (rarely 

 pentameral, heptameral, or odameral) arrangement of septa. 



1 Literature : Pratz, E. , Ueber die verwandtschaftliche Beziehungen einiger Korallengattimgen, 

 etc. Palaeoutogr. 1882, vol. xxix. — Freeh, F. , Die Korallenfauna derNordalpinen Trias. Palaeontogr. 

 1890, vol. xxxvii. — British Museum Cat. of Madreporarian Corals, vol. i. by George Brook, 1893, 

 vols, ii.-vi. by H. M. Bernard, 1896-1906. — Volz, W., Die Koralleu der Schichten von St. 

 Cassiau in Siid-Tirol. Palaeontogr. 1896, vol. xliii. Felix, J., Antliozoen der Gosauschichten 

 in den Ostalpen. Palaeontogr. 1903, vol. xlix. — Duerden, J. E., The Coral Siderastrea, etc. 

 Carnegie lust. Wash., 1903, Pub. No. 20.— Lang, W. D., Growth-Stages in the Coral Genus Para- 

 sniilia. Proc. Zool. Soc. London, 1909, pt. ii. — Parana, C. F., La Fauna coralligena del Cretaceo 

 dei Monti d' Ocre nell' Abruzzo. Mem. Com. Geol. Ital., 1909, vol. v. (See also ante, p. 74). 



