302 DE. A. VATJGHAN ON THE EAUNAL SUCCESSION [May I906, 



The foregoing determinations are subject to but a small error of 

 identification. 



Correlation of the ' CyatJiaxonia-Beds' with some 

 part of the Upper Dibunopliyllum-Zone of the Avonian 

 of the South-Western Province. — For the purpose of cor- 

 relation the facts may be marshalled thus : — 



(i) As regards the Corals : — 



(1) Cyathaxonia and Cladochonus are unknown in the South- Western 

 Province. 



(2) Amplexi-Zaphrentis and Zaphrentis aff. Enniskilleni abound in the 

 upper D-beds of Oystermouth (Gower). 



(3) The Clisiophyllids are comparatively scarce, and do not exhibit a 

 very advanced type of structure, the Caninoid type being predominant. 

 They cannot be actually matched from the South- Western Province, but 

 would appear to have reached at least as advanced an evolutionary stage 

 as our D-, forms. 



(ii) As regards the Brachiopods : — 



(1) With the exception of the fimbriate and pustulose Producti, the 

 convex -papilionaceous Chonetes, Schizophoria resupinaia,Athyris glabristria, 

 Athyris cf. expansa, and Camarophoria aff". isorhyncka, the brachiopod- 

 fauna of the Cyathaxonia-lBed.s may be said to be completely diagnostic of 

 the upper D-beds of the South-Western Province. The absence of the 

 small Chonetes characteristic of e and the rarity of scabriculate Producti 

 suggest, for the ' Cyathaxwiia-TSeds,' a level at the top of D 2 , below the 

 very top of the Avonian of the South-Western Province. 



(2) In the South-Western Province convex-papilionaceous Chonetes and 

 Athyris cf. expansa do not transgress D 1 . 



Fimbriate and pustulose Producti, as well as Athyris cf. glahristria, have 

 not been recorded above S r 



Camarop>horia isorhyncha (closely related, but not identical with the 

 Rush form) is known only from the base of S r 



Schizophoria resupinata is unknown above the base of 0. 



Syringotltyris subconica is markedly convergent with Cyrtina septosa, a 

 species which I have recently found in D l of Lydstep (Tenby). Eegarded 

 from an evolutionary standpoint, S. subconica could be derived from the 

 gens of 8. cf. laminosa by convergence with Cyrtina septosa; By ring o~ 

 ihyris cf. laminosa is unknown above S r 



The whole evidence, when proportionally weighed, seems to point 

 with the greatest probability to the Upper BibunojjJiyllum-age of 

 the ' Cyathaa?onia-Beds,' but the exact position which they occupy in 

 that subzone is not as yet absolutely fixed. 1 



1 It is very important to appreciate the fact that, during the Upper Seminula- 

 period, the whole of the South-Western Province was subject to special con- 

 ditions, and therefore exhibited a limited and peculiar fauna. In C and S x we 

 can watch the birth and early mutation of all the gentes characteristic of Upper 

 Avonian time ; but, during the Lower Seminula-yeriod, most of these groups 

 were banished from the area, to continue their evolution elsewhere. It was not 

 until the close of the Pibuno2)hylluin--period that the normal conditions were 

 restored, and the complete fauna returned. It is, therefore, impossible to study, 

 from the evidence presented by the South-Western Province alone, the mutations 

 to which each gens was subject during S and J) l time ; and so too it is 

 impossible to appreciate the exact time-value of the variations which can be 

 observed in specimens from other areas. 



