28 R. G. Carnit/iers — A Itevision of some Carboniferotis Corah. 



Slates of CO. Dublin, correlated by Dr. Vaughan with subzone Zo. 

 But in other areas the species is found on different horizons. For 

 instance, in the Colne-Clitheroe district it is found in limestones very 

 probably of Upper Visean age, and is there rather common and quite 

 typically developed. Again, in Scotland good examples seem very 

 rare, but almost the only specimens yet obtained were found in the 

 Millstone Grit near Glenboig, in a band of cement lying not far below 

 the junction of the Upper and Lower Carbonifei'ous floras. Never- 

 theless, no really typical examples have so far been found in the 

 underlying and richly fossil if erous Lower Limestone group (Visean) 

 and not one in the Tournaisian Cement Stones, where other small 

 Zaphrentids are not uncommon in certain localities. 



With the evidence at present befoi'e us the conclusion seems 

 justifiable, therefore, that Z. omalium has an extensive vertical range, 

 biit may be locally confined to definite horizons. 



Zaphrentis omaliusi, var. ambigva, var. no v. (Plate IV, 

 Figs. 5 and 6.) 



External CnAiiiCTERS. 



Dr. Vaughan has noticed the occurrence of this variety in the Rush 

 Slates, and has drawn attention to the chief distinction from the Rush 

 Zaphrentids (see Q, J.G.S., vol. Ixii, 1906, p. 314, first paragraph on 

 "variants of the Rush Zaplirentis "). 



Corallam similar in shape and external ornamentation to Z omalimi. 

 The ca/i/x is also similar to that seen in Z. omaliusi, save for the large 

 size of the counter fossida lying on the concave side of curvature of 

 the coral. 



Internal Characters. 



(a) Transverse Sections. — The chief characteristic of this variety is 

 at once seen to lie in the counter fossula. This is developed to an 

 extraordinary degree, more so than in any coral with Avhich I am 

 acquainted. Though initially small, for sections taken near the tip 

 of the coral are essentially the same as similar ones in the normal 

 species (compare Fig. ba with Fig. \a, PI. IV), this counter fossula 

 becomes increasingly apparent during the growth of the coral. The 

 two septa forming the sides become more or less parallel, and in the 

 final stages of growth an expansion occurs at the inner end, varying 

 in degree with different specimens, and giving, in sections cut just 

 under the calyx of an adidt, a broad club-shaped outline to the 

 counter fossula (PI. IV, Fig. 6). The counter septum extends 

 down the centre; of this fossula throughout, and never becomes 

 shortened to any appreciable extent, even in the calyx itself. 



The cardinal fosmla, on the other hand, is comparatively small and 

 inconspicuous. The septa forming the sides also show a tendency to 

 parallelism, though this appearance is naturally modified if the section 

 happens to show the incoming of new septa (a feature never seen in 

 the counter fossula). 



In accordance with the extreme development of the counter fossula, 

 the fusion of the septa of each of the four quadrants is very marked, 

 and takes place further from the centre than in the normal species ; 



