102 COELENTERATA ANTHOZOA SUB-BRANCH n 



Corallum commencing with prostrate basal network similar to Aulopora. 

 Numerous species ranging from Silurian to Carboniferous. 



Chonostegites, E. and" H. Corallum massive; cylindrical corallites con- 

 nected by horizontal, hollow, laminar expansions into which the endothecal 



tissues are directly continued ; tabulae oblique, cystoid. 



Devonian. 



Thecostegites, E. and H. Corallum encrusting ; corallites 



short, cylindrical, and connected by thick horizontal plates. 



Tabulae approximately horizontal ; septa twelve in number, 



represented by marginal ridges. Devonian. 



Family 4. Halysitidae. Milne-Edwards and Haime. 

 Chain corals. 



Corallum composed of long, cylindrical, laterally compressed 

 corallites, which are joined to one another only along the more 

 constricted edges, and form free, vertical, intersecting, and an- 

 astomosing laminae. Wall thick, covered on free sides by wrinkled 

 Liisp <f Silurian' -"oott- epitheca ; tabulae numerous, horizontal^ or concave ; septa repre- 

 land. Natural size. sented by vertical ridges or rows of spines, in cycles of twelve, 



sometimes entirely absent. Increase by stolonal gemmation. 



The single genus Halysites, Fischer (Catenipora, Lam.), (Fig. 182), comprises 

 two groups of species ; those in which the corallum is composed throughout of 

 corallites of .equal size (H. escharoides, Lam. sp.), and others in which any two 

 of the larger corallites are separated by the intervention of a single smaller, 

 closely tabulate tube (H. catenularia, Lin.) Ordovician and Silurian; maximum 

 in Silurian. 



Family 5. Chaetetidae. Milne-Edwards and Haime. 



Massive cwalla, composed of fine, subequal, tubiform corallites, contiguous on all 

 sides. Calices rather irregular in shape, one diameter slightly greater than the other. 

 Walls thoroughly amalgamated, common to adjacent corallites, imperforate, apparently 

 composed of closely arranged, ankylosed vertical columns, which terminate at the surface 

 in hollow prominences. Septa absent, but one or two tooth-like projections often observ- 

 able in sections. Tabulae horizontal, remote or abundant. 



AH the forms belonging to this family are extinct, and occur chiefly in the 

 Ordovician, Silurian, Devonian, and Carboniferous systems ; but they are also 

 found sporadically in the Trias, Jurassic, and Cretaceous. They are important 

 as being largely concerned in the formation of Palaeozoic coral reefs, especially 

 during the Ordovician. Milne -Ed wards and Haime regarded them as An- 

 thozoans, Rominger and Lindstrom as Bryozoans ; while Dybowski, though 

 admitting their resemblance to certain Bryozoans, emphasised their affinities 

 with the Favositidae. By Nicholson they were assigned to v the Octocoralla, for 

 the reason that the corallites frequently exhibit a dimorphous character the 

 same as in Heliolites and Heliopora, besides agreeing in their microscopic 

 structure with Heliolites ; while in addition they possess well-developed tabulae 

 and imperforate walls, and increase by intermural gemmation or by fission. 

 Nevertheless, their resemblance to certain of the cyclostomatous Bryozoans 

 (Heteropora) is fully recognised by Nicholson, and insisted on by Ulrich. 



Chaetetes, Fischer (Figs. 183, 184). Corallites long, thin-walled, prismatic, 



