82 COELENTERATA CXIDABIA SUB-BRANCH n 



same time mark off the boundaries between which new cycles of successively six, 

 twelve, twenty-four septa, etc., are inserted. The septa of any cycle are usually 

 all of about the same length and thickness, those of the later cycles being almost 

 invariably of lesser proportions than those of the earlier. This law of septal 

 growth, however, which was first accurately determined by Milne-Edwards and 

 Haime (Fig. 130), is by no means strictly adhered to. Irregularities in the 

 growth of new septa may result in a penta-, hepta-, or octameral arrangement. 

 Reproduction takes place either sexually, when separate individuals are pro- 

 duced ; or asexually, by means of lateral or basal gemmation ; or by fission. In 

 composite coralla, the individual corallites are sometimes united by a common 

 coenenchyma. Endothecal structures are frequently present in the form of 

 synapticula, dissepiments, and tabulae. 



The order of stone corals or Madreporaria (Zoantharia sclerodermata) was 

 divided by Milne-Edwards and Haime into five sub-orders : fiugosa, Tabulata, 

 Tubulosa, Perforata, and Aporosa. Of these, the Itugosa have been elevated by 

 Haeckel into a separate sub-class under the name of Tetracoralla. The groups 

 Aporosa and Perfomta are called Hexacoralla ; while the affinities of the Tabulate 

 (with which the Tubulosa 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 Octocoralla, 

 and some to the Hydrozoa and Bryozoa. 



[Miss Ogilvie, D.Sc., will shortly publish a work on the "Structure and 

 Classification of Corals," in which the subdivisions of the Madreporaria into 

 Tetracoralla and Hexacoralla are entirely abandoned, on the ground that the tetra- 

 meral septal system is merely an ancestral feature strongly marked in certain 

 of the older families, while hexameral septal symmetry is but one of many forms 

 of radial symmetry (pentameral, octameral, decameral, dodecameral, etc.), 

 developed in the course of time within this group of corals. The further sub- 

 division of Hexacoralla into Aporosa and Perforata is also discontinued by Miss 

 Ogilvie, who classifies the whole of the Madreporaria (" stone corals ") into a 

 number of families of equal rank. These are : Zaphrentidae, Cyathophyllidae, 

 Amphiastraeidae (a new family of Palaeozoic Recent age, including Stauria, 

 Columnaria, Pinacophyllum, AmpJiiastraea, Aplosmilia, Euphyllia, etc.), TurUnolidae 

 (including the Cyathaxonidae and Trochosmilinae), Oculinidae, Pocilloporidae (in- 

 cluding the Stylophorinae with the genera Astrocoenia and Stephanocoenia), Madre- 

 poridae (including the Turbinarinae), Stylinidae, Astraeidae (excluding the Eus- 

 milinae, Edw. and H.), Fungidae (including the Thamnastraeinae), Eupsammidae 

 (including the Stylophyllinae, Epistreptapliyllum, Diplaraea, etc.), Archaeocyathidae, 

 and Poritidae. THE AUTHOR.] 



rder 1. MADREPtRARIA. Milne-Edwards. 



Radially symmetrical sclerodermous corals with typically hexameral (rarely penta- 

 meral, heptameral, or octameral) arrangement of septa. 



Sub-Order A. APfROSA. Milne-Edwards and Haime. 



Septa and theca compact ; inter septal loculi usually partitioned off by dissepiments 

 oi' synaptioles, more rarely by tabulae, seldom empty throughout. Theca either in- 

 dependently secreted, or formed by fusion of the septal edges, or absent. 



