558 MR. E. E. L. DIXON AND DE. A. VATJGHAN ON [Nov. I9II, 



I. The right-hand specimen presents the typical characters of 



Dibunophyllum 6, namely : — 



A circular, ill-bounded central area, which is completely bisected by 

 a somewhat flexuous mesial plate ; the general structure of the area is 

 simply reticulate. 



A loosely vesicular external ai'ea, with a very ill-defined inner boundary. 



Extremely short minor septa. 



II. The left-hand specimen illustrates the early form of Dibuno- 

 phyllum \p, with which it agrees in the following characters : — 



The cuspidate boundary of the central area. 



The suggestion of Aspidophylloid characters : that is (1) the abrupt 

 termination of the mesial plate within the central area ; (2) the fact 

 that the lamella? start from the boundary of the area, and fall short of 

 the mesial plate. 



The close-set vesicles of the external area and the well-defined inner 

 wall. 



The elongate minor septa, which usually extend completely across 

 the external area. 



The differences are mainly of degree only, namely : — 



The early form is cylindrical (convergent on Dibunophyllum 6) ; 

 Dibunophyllum $ is conical. 



The sharp, cuspidate boundary of the central area and the Aspido- 

 phylloid characters are more strongly marked in Dibunophyllum i//. 



A purely vesicular peripheral area is practically absent from the D l 

 form. 



This early form of Dibunophyllum \p is not uncommon at several 

 localities in the South- Western Province. 



CYATHAXONTDS. 



' Cyathaxonia ' sp . 



Compare ' Cyathaxonia'' aff. costata, figured in Rush Paper, pi. xxix, fig. 5. 



Two poorly preserved specimens, from the base of D 2 _ 3 in the 

 North Colts Hill Quarry, were collected and kindly presented to 

 me by Mr. Underhill ; their matrix is rottenstone. Both specimens 

 show the calyx, and one of them shows, at its lower end, the 

 highly-vaulted under surface of a tabula. 



Radiating from the wall are 26 septa, short, thick, and of equal 

 length, except that the fossula is marked by a single short cardinal 

 septum. 



The floor of the calyx rises centrally into a tall spear-shaped 

 columella, which is laterally compressed and crested like a helmet ; 

 the lateral surfaces of the .columella are roughened by the external 

 edges of the numerous close-set longitudinal lamellae. By rubbing 

 down the columella, the lamellae are seen to radiate inwards 

 towards the mesial plate which is the downward continuation of 

 the crest. 



After further rubbing down, through a very short distance, the 

 section cuts an underlying tabula in a roughly concentric curve, 

 and from this curve a second setof lamellae radiate inwards towards 

 the mesial plate. 



