Vol. 62.] IN THE CAEBONIFEKOUS KOCKS AT RUSH. 315 



Zaphkentis aff. Enniskilleni, Edwards & Haime. (PI. XXIX, 

 fig. 2.) 



This gens includes a large number of closely -related forms which 

 occur abundantly in the uppermost Avonian, and are diagnostic of 

 that level. 



The form is always conical and usually cornute. 



The septa are strongly separated into three groups, namely, 

 two fossular groups and one antifossular group. The fossula is 

 extremely-well developed, and the lateral breaks are usually very 

 strong. The tabulse are, however, Amplexoid; the fossular septum 

 is either absent or very short. 



To this gens may be referred the corals figured by James 

 Thomson in his pi. vi, figs. 4 & 10. 1 



Specimens are common in the Cyathaxonia-Beds of Ptush, and 

 afc the same level at Bradbourne (Derbyshire). In the South- 

 Western Province the gens is equally prolific in the uppermost 

 Avonian of Gower. 2 



Amplexi-Zapheentis (subgenus nov.). (PI. XXIX, fig. 7.) 



Thomspn, Proc. Phil. Soc. Glasgow, vol. xiv (1882-83) pi. vi. figs. 3, 9, 

 &13. 



Eorm. — Conical, straight or curved. 



Septal characters exhibited in a horizontal section. — 

 The septal grouping is remarkably different at different stages of 

 growth in the same individual : 



(1) In the early stage. The septa are few in number and so closely approxi- 

 mated that the interspaces are extremely narrow ; they are attached to the 

 thick wall by very broad bases, and taper gradually towards the centre without 

 bending. 



Tbe symmetry is strongly bilateral, the axis of symmetry being defined by 

 two collinear septa which are respectively the longest and shortest of the septal 

 series. 



(2) In the intermediate stage. Many of the septa become shorter ; broad 

 tabulas are developed ; and a fossula is marked out, both by a break in the septal 

 series, and by a shallow depression of each tabula. 



In this stage two lateral and opposite septa often stretch across the corallum 

 to meet in the centre, and separate an antifossular group of short septa from 

 the two lateral groups on either side of the fossula. At the same time, broad 

 lateral gaps may be developed in the septal sequence. Pig. 7 (PL XXIX) 

 illustrates a variant of this description, and a comparison of the figure with 

 fig. 2 of the same plate will show how deceptive is the convergence between 

 this stage of Amplexi-Zaphrentis and the group of Zaphrentis aff. Enniskilleni, 

 notwithstanding the fact that the early and late stages of the two groups are 

 entirely distinct. Thomson's fig. 3, above cited, appears to be a typical example V/ 

 of the intermediate stage of an Amplexi-Zaphrentis. 



(3) In the late stage. The septa all become short ; fiat tabulae extend com- 

 pletely across the corallum, but bend down near the wall. The fossula is a 



1 ' Corals of the Carboniferous System of Scotland ' Proc. Phil. Soc. Glasgow, 

 vol. xiv (1882-83). 



2 I am at present engaged on the detailed study of these specimens, and 

 consequently defer a more exhaustive account of the relationships of the 

 gens. 



