392 THE AVONIAN OF BURRINGTON COMBE. [Aug. I9II, 



1 Fig. 4. MiclieUnia Jconincki nom. nov. = M. tewuisepta de Kon., non (Phill.) 

 (p. 372). The vertical section of a disconnected corallite from Z,. 



5. Carcinophyllum 9 Vaugban (p. 377). From the lower part of S 2 . 



6. Cyathophyllum aff. nmrehisoni E. & H. (p. 379). An aberrant variant 



from the top of S 2 . 



7. Dlphyphyllum sp., convergent Koninckophyllum 9 (p. 380). From D x . 



8. Syringothyris laminosa (de Kon.), non (M'Coy) (p. 383). From 



Horizon y. 



Discussion. 



Dr. T. F. Sibly congratulated the Authors on their detailed 

 revision of this magnificent section. In the description of the 

 section published by him in 1905, the faunal divisions recognized 

 were substantially those maintained in Dr. Vaughan's Bristol paper. 

 But later researches had greatly modified that original classification, 

 and certain alterations were very conspicuous in the case of this 

 section. He drew special attention to the change in the delimitation 

 of Zones Z & C. Horizon y, as originally defined by Dr. Vaughan, 

 was characterized by the abundance of Caninia cylindrica, and was 

 recognized as an horizon of faunal overlap between the two zones. 

 But this horizon, so clearly defined in the Burrington sequence, was 

 now placed high up in C x , the designation ' Horizon y ' being trans- 

 ferred to a much lower level characterized by Caninia patula. At 

 the same time, Zone C became greatly expanded at the expense 

 of Z. 



With reference to the Seminula Zone, and the relatively very 

 small thickness of S x as here defined by the Authors, the speaker 

 enquired what was the precise evidence relied on for separating S 

 from S . This zone was much better displayed in the Cheddar 

 Gorge than at Burrington. At Cheddar, only 2 or 3 miles distant, 

 a typical S 1 fauna occurred some 300 feet above the base of the 

 zone, and JS 1 was little, if at all, inferior in thickness to S 2 . A 

 remarkable fact, in his opinion, was that this Upper S 1 horizon at 

 Cheddar showed a strong development of chert and an abundance 

 of Litliosbrotion martini in silicified masses, features identical with 

 those of certain beds in the Burrington section included by the 

 Authors in their S 3 . 



With regard to the generic position of ' Syringothyris' laminosa, 

 he mentioned that he had recently collected some well-preserved 

 internal casts of this shell from C in the Mitcheldean district. These 

 specimens showed no trace of a true syrinx, but exhibited a peculiar 

 modification of the mesial septum in the pedicle- valve. 



Prof. Garwood also spoke, and Dr. Vaughan briefly replied on 

 behalf of the Authors. 



