Vol. 67.] THE AVONIAN OF BUKR1NGTON COMBE. 363 



TOUKNAISIAN or LOWER AVONIAN. 



Cleistopoba Zone (K). 



K,: 



The lower portion is an Ostracod-Modiolid phase, capped by the 

 * Bryozoa Beds.' 



The upper portion consists of normal limestone-shales. 



Corals : — 

 None recorded. 



Brachiopods : — 



Choneies cf. buchiana de Kon., early mutation. Very abundant at the 



base of tbe upper portion, as in the Avon section. 

 Chonetes cf. laguessiana de Kon. Abundant at certain levels in the 



lower portion. 

 Small Rhyncbonellids, in part referable to Camarotcechia mitchel- 



deanensis Vaughan. 

 Eumetria sp. and Producius cf. bassus Vaughan are recorded by 



Dr. T. F. Sibly. 



K 2 : 



Only the uppermost part of this subzone is exposed, and that 

 badly, along the stream in Goatchurch valley. 



Corals : — 



Zaphrentis delanouei E. & H., Carruthers. Very rare and only at the 



top. 



Brachiopods : — 



Spiriferina cf. octoplicata (J. de C: Sow.). Rare. 

 Together with most of tbe species recorded below at Horizon (3. 



Zaphrentis Zone (Z). 



Cleistopora being unknown, and Zaphrentis delanouei at least 

 represented in the uppermost beds just described, it might seem 

 logical to include the upper part of these beds in Z rather than 

 in K; comparison, however, with neighbouring areas where the 

 fauna is better known, together with the change of lithological 

 character, suggest the division here adopted. 



[It would be too hasty a conclusion to infer that the incoming of 

 Zaphrentis was solely due to the change of conditions represented 

 by the change of lithology ; for in other localities (for instance, 

 Llanvaches), where K and Z have a continuous lithological 

 character, the establishment of Zaphrentis is delayed until ap- 

 proximately the same time as at Burrington. The facts point 

 rather to a widespread and zonally-simultaneous introduction by 

 migration.] 



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