FAUNAL SUCCESSION OF THE UPPER BERNICIAN 6oi 



L.floriformis. In Northumberland this species is rare, but 

 Z. diiplicafa, var. conaxis, is common. 



The branching out into numerous variants, which both 

 Dibunophylhiiii and Koninckophylhim exhibit, illustrates the 

 instability which frequently precedes extinction. 



DiphyphyUnm reaches its acme of development in D. 

 dianthoides, which is only foreshadowed in the D2 of the 

 South-West Province. 



On the other hand one of the variants of Koninckophyllum 

 is less highly developed than the D2 species of the South- 

 West Province, and is but little advanced on the Di form. 

 Also Cyclophylhnn aff. pachyendothecum is not much more 

 advanced than the form in Di. 



The rich coral fauna which reaches its maximun develop- 

 ment in IVa is represented by exaggerated and decadent 

 forms in IVb and IVc. 



IVb.— (Dy). 



The tendency in the Dibunophyllids towards Aspidophylloid 

 structure, already marked in IVa, reaches its highest 

 development in the Aspidophyllum of the Thornbrough Lime- 

 stone. Dibiinophyllu?n 7nuirheadi (typical) is, nevertheless, 

 abundant in this limestone.* A new genus of Cyathophylloid 

 Dibunophyllum, which occurs in the Robsheugh Limestone, 

 shows convergence with Caiiinia cf. cormicopice and Densi- 

 phyllmn in the regularly spaced interseptal intersections in 

 the large medial area. 



IVc— (Dy). 



The index of IVc is Dibunophylhim muirheadi (mut. cf, 

 Dib. ip). The genus Ko7nnckophylhL?n is represented by a 

 loose-structured, irregular and decadent form. The Cyatho- 

 phyllufH characteristic of the horizon has the vaulted vesicular 

 tabulae of Cyathophylhwi regiufn, but exhibits reversion in the 

 fact that the tabulee are only partially replaced by vesicles. 



* lu Thornbrough Quarry, Corbridge. 



