E. G. Carnithers — A Revision of some Carhoniferous Corah. 29 



the fused ends meet in the centre of the coral. Apart from this fact 

 the septa are certainly less flexuous and more uniformly curved than 

 in the normal species. 



A majority of the specimens I have examined also show decidedly 

 thinner, and sometimes more closely packed, septa than in Z. omaliusi. 

 This does not, however, seeni at present to be a character of any great 

 value. Exceptions certainly exist with strong septa fusing to a dense 

 mass in the centre of the coral. 



(b) Vertical Sections. — As in Z. omaliusi, though the depression of 

 the tabulae at the counter fossula is proportionately greater. 



Localities. 

 Upper (?) Visean : Horrocksford Quarry, Clitheroe (common). 

 Tournaisian : Rush Slates ( R 4 «, R 8 a, and especially R 6 3, for 

 position of which see Q.J.G.S., vol. Ixii (1906), p. 276, fig. 1). 



Remarks. 



The diiferentiation oE this variety from Z. omaliusi, lying chiefly in 

 the character of the cardinal and counter fossulae, has been sufficiently 

 dealt with in the foregoing description. In the possession of 

 a prominent fossula, divided even in the calyx by a long septum, 

 Z. omaliusi, var. amhigua resembles Z. lyliillipsi, as described bj' 

 Milne-Edwards & Haime ; but the latter has its prominent fossula on 

 the convex instead of the concave side of the corallum, while the 

 epithecai characters are very different. It also seems probable that 

 the prominent fossula of Z. pMllipsi is a cardinal rather than 

 a counter fossula, and the same distinction immediately separates 

 Z. delanouei from Z. omaliusi, var. ambigua, to which it otherwise has 

 a great resemblance. 



At both of the known localities the variety is found in association 

 with normal examples of Z. omaliusi, and although the two are 

 easily separable in typical examples they are united by intermediate 

 forms whose reference to one or the other of the two corals is often no 

 easy matter ; and, indeed, it will be seen on comparing Eigs. 1 a and 

 ba on PI. IV that the young stages of the species and its variety are 

 essentially identical. 



JDistrihution. 



I am at present acquainted with only two localities for this 

 curious variety. These seem, however, to lie on very different 

 horizons. That in the Rush Slates has been correlated by 

 Dr. Yaughan with the Upper Tournaisian subzone Zg of the South- 

 western Province. The other locality is Horrocksford Quarrj^, 

 Clitheroe, where examples are abundant in certain shaly partings 

 between beds of massive limestone containing a brachiopod fauna, 

 indicating, according to Dr. Wheelton Hind, an Upper Visean horizon 

 somewhere about the base of D or the top of S. These correlations, 

 therefore, if correct, indicate a considerable vertical range for the 

 coral. 



Z. OMALIUSI, var. densa, var. nov. (Plate IV, Figs. 7 and 8.) 

 Shape, dimensions, and epithecai characters as in Z. omaliusi. The 

 calyx also is very similar, save that the radial disposition of the septa 



