R. G. Carruthers — A Revision of some Carboniferous Corals. 163 



Fig. 1) where such septa may be found even when the dissepimental 

 zone, marking a mature stage of growth, is well established. 



The foregoing paragraphs are intended to demonstrate that the 

 development of the septa in the calyx is not of specific value in 

 this species, but is largely dependent on two factors, whose relative 

 importance must be expected to vary in different specimens. There 

 remain, however, other data amply sufficient for a recognition of the 

 species, and these will be noticed after describing the internal 

 characters. 



Average dimensions. 



Height of fully grown adult, at least 6 cm. (a considerably greater 

 length is sometimes attained; see Diag. E, Fig. 6). Diameter of rim 

 of adult calyx, 1"5 to 2 cm. jN^umber of major septa to above 

 diameters, 32 to 33 respectively. (Diameters of 2-5 to 2-8 cm., with 

 37 septa, are occasionally reached.) 



Internal Chaeactees. 

 • (a) Horizontal sections. 



1 . Nature of the septa. — The major septa are very thin ; their inner 

 ends taper to a fine point and are often curiously twisted ; there is, 

 however, occasionally a slight thickening at the inner end of the long 

 counter septum. The cardinal septum dwindles in length at an early 

 stage, and soon becomes very short. 



2. Grouping of the septa. — There is usually a slight, but distinct, 

 curvature, concave to the cardinal fossula. In the lower, conical part 

 of the corallum, the septa are much thickened by a deposit of stereo- 

 plasma, which at first affects them all, but as growth proceeds this 

 becomes restricted to those septa in the two cardinal quadrants, and 

 finally dies away altogether. The deposit characterises the vermicu- 

 laris and dumonti phases (i.e. in which septa continuously reach 

 the centre of the coral) and transverse sections of such parts compare 

 well with each other (PI. YI, Figs. \h to Id and Figs. 2a to 2d). 

 But when the septa become amplexoid, it will be seen from Diag. F, 

 Fig. 1, that the length of the septa in transverse sections largely 

 depends on the relation of the section to the nearest tabula, for 

 a section may show either very short or very long septa, according 

 as it is cut immediately underneath, or immediately above, one of the 

 tabulae. 



It will be apparent also that a section cut between well-separated 

 tabulae will usually show longer septa than one cut between closely 

 set tabulae (Diag. F, Fig. 1, B). 



Since amplexoid septa may appear at any stage, transverse sections 

 of this coral should be judged relatively, the appearance of 

 a section being independent of the diameter. Thus, in a broad, 

 rapidljr expanding form of the coral (Diag. E, Fig. 1) sections 

 illustrating the dumonti phase may be twice the original size of 

 the enlarged figures on PL YI, Figs. 2a to 2d, and contain many 

 more septa ; conversely, with forms acquiring the cylindrical habit 

 at an early stage, sections in the dumonti phase vn.o.j appear when but 

 few septa are developed. 



