I 



Fia. 184., 



BCLAss III TABULATA— CHAETETIDAE 117 



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 

 restricted edges, and form free, vertical, intersecting and anas- 

 tomosing laminae. Wall thick, covered on free sides by wrinUed 

 epitheca ; tabulae numerous, horizontal or concave ; septa repre- 

 sented by vertical ridges or rows of spines, in cycles of twelve, 

 sometimes entirely absent. Increase by stolonal gemmation. 



The unique genus Halysites Fischer (Catenipora Lam.) 

 (Fig. 184), comprises two groups of species ; those in 

 which the corallum is composed throughout of coral- 

 lites 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 , . 



, ^-r , . ^ . \/^i-. T ri", • . Halysites catemilana 



{II. catenmana L\nn. sp.) Urdovician and JSilunan ; maxi- (Linn.). Siiurian ; Got- 

 mum in the Siiurian. ^^"^- Natural size. 



Family 5. Chaetetidae Milne Edwards and Haime. 



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

 sides. Calices rather irregulär in shape, one diameier slightly greater than the other. 

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

 composed of closely arranged, anJcylosed vertical columns, which terminale at the 

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

 often observable in sections. Tabulae horizontal, remote or abundant. 



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

 Ordovician, Siiurian, Devonian and Carboniferous Systems ; but a few are 

 also found sporadically in the Trias, Jura and Cretaceous. They are largely 

 concerned in the formation of Paleozoic coral reefs, especially during the 

 Carboniferous. Milne Edwards and Haime regarded them as Anthozoans, 

 Rominger and Lindström as Bryozoans, while Dybowski emphasised their 

 affinities with the Favositidae. By Nicholson they were assigned to the Octo- 

 coralla, 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. Many genera and species formerly 

 included under this family are now assigned to the Bryozoa. 



Chaetetes Fischer (Figs. 184«, 1846). Corallites long, thin-walled, prismatic, 

 polygonal, all of one kind, and multiplying by fission. Uncompleted fission 

 of the tubes often indicated in section by tooth-like projection extending 

 into the visceral Chamber. Walls structureless, without dark median line ; 

 tabulae complete, remote. Very abundant in Lower Carboniferous ; found 



