﻿Vol. 6 1.] SEQUENCE IN THE BRISTOL AEEA. 249 



sequence in the two areas. All the statements refer equally to 

 either area. 



1. The Carboniferous Limestone starts with a Modiola-ostraeod 



phase, which includes an identical horizon (Horizon «). 



2. The Cleistopora-Zone can be differentiated into two snbzones 



K T and K,, characterized by the same faunal assemblages in 

 the two areas. Striking constituents, such as Productus 

 bassus and Chonetes ' Buchiana,' occur in both areas. The 

 period of entrance, the gradual increase in numbers, and 

 the position of maximum in the case of the commonest 

 constituents is the same (for example, Spirifer aff. clathratus). 



3. The same species, in identical forms, are associated in Z v and 



the forms decline in numbers when traced through Z 2 . 



4. Ampleocus attains its maximum before Oaninia in Z 2 . 



5. Zaphrentis is common throughout the Zaphr entis-Zone, but is 



rare in all higher beds. It attains its maximum at the top 

 of Z 2 , where it is represented by the two common species. 

 In Z 1? Zaphrentis aff. Phillipsi is the only form met with. 



6. Schizophoria resupinata is associated with Gliothyris gla- 



bristria. 



7. Oaninia is enormously abundant at the top of the Zaphrentis- 



Zone and extends on into C. 



8. Michelinia has its maximum in Z (fide T. F. S. for Burrington). 



9. OrtJiotetes erenistria is quite common throughout the Tour- 



naisian, but is rare above that level, although occasionally 

 found up to the Dibunophyllum-Zone. 



10. Chonetes cf. hardrensis occurs abundantly up to the top of Z 2 , 



but yields its predominance in higher beds to Chonetes 

 papilionacea, by which it is soon entirely replaced. 



11. At the base of C there is a band crowded with OrtJiotetes 



erenistria and Chonetes cf. comoides in association. 



12. Cyathophyllum ty is enormously abundant at the top of C, 



associated with Better ophon sp., OrtJiotetes erenistria, and 

 Syringothyris aff. laminosa. 



13. Productus Q is extremely prolific at the bottom of the Seminula- 



Zone (where, however, Lithostrotion and Seminula are rare 

 at Burrington). 



14. Lithostrotion Martini abounds in the middle of the Semhada- 



Zone, where it is associated with Productus and JSeminula. 



15. Clisiophyllids enter in small numbers in the upper part of 



the Seminida-Zone. 



16. The fauna of the Dibunophyttum-Zone is identical in the two 



areas. 



The points of difference, though small, are of great interest ; 

 they may be summed up in the statement that, when compared 

 with the Bristol area, the coral-fauna in the Tournaisian of the 

 Mendips is accelerated relatively to the brachiopod-progression. 



(1) In the Mendip development Michelinia occurs commonly with 

 the assemblage of brachiopods characteristic of Z x , whereas in the 



