360 MR. T. E. SIBLY ON THE CARBONIFEROUS [May 1 906, 



teristic of the Kidwellian ; but early forms of Productus aff. Cora 

 occur very rarely in Z, and commonly in C. 



The following coral-groups pass up from the Clevedonian into 

 the Kidwellian : — 



8yringopora. The sole essentially-Clevedonian form is Syringopora 9. S. cf. 

 reticulata characterizes the uppermost Clevedonian, bat persists into the base 

 of the Kidwellian. The types represented by S. cf. distans, 8. cf. genicidata, 

 and 8. cf. ramulosa are essentially Kidwellian, although 8. cf. distans occurs 

 rarely in 0. 



Caninia cylindrica is essentially an Upper Clevedonian form, which persists 

 into the base of the Kidwellian. 



Cyathophyllum <p characterizes the uppermost part of the Clevedonian and the 

 base of the Kidwellian. 



Campophyllum occurs commonly in the uppermost part of the Clevedonian 

 and the Upper Kidwellian. 



The following brachiopod-groups pass up from the Clevedonian 

 into the Kidwellian : — 



Productus cf. semiretiadatus. 



Athyris cf. glabristria. This group ranges throughout the greater part of the 

 Clevedonian, and persists into the Lower Kidwellian. 



Athyris cf. expansa, constitutes a distinct link between the uppermost 

 Clevedonian and the Kidwellian. 



Orthothetes aff. crenistria is a very important link ; but, whereas it is 

 enormously abundant throughout the Clevedonian, it is rare above the lowest 

 part of the Kidwellian. 



Bhipidomella aff. Michelini is very abundant throughout the main part of the 

 Clevedonian, and persists into the base of the Kidwellian. 



Chonetes cf. papilionacea constitutes an important link between the Upper 

 Clevedonian and the Lower Kidwellian. 



8erninula is an essentially-Kidwellian genus ; but 8. ambigua is common 

 in the upper part of C, and 8. aff. ficoides occurs rarely in the uppermost beds 

 of the Clevedonian. 



YI. Summary. 



(1) The faunal sequence in the Avonian (Carboniferous Lime- 

 stone) of the Mendip area is essentially similar to that in the 

 Bristol area. 



(2) The separation of a lower division, the Clevedonian, from an 

 upper division, the Kidwellian, with the line of separation drawn 

 at the top of the Syringothyris-Zone, is well-defined, and fully 

 justified by the distinctness of the lower and upper faunas. 



(3) The most important features of the Mendip sequence, when 

 compared with the sequence in the Bristol area, are as follows : — 



(a) The great expansion in thickness of the Zaplirentis- and 



Syringothyris-Zones. 



(b) A relative acceleration of the coral-fauna on the brachiopod- 



fauna, exhibited in the Zaphrentis-Zone. 



(c) The continuously-fossiliferous sequence which extends from 



the top of the Zapltrentis-Zoiae to the base of the Seminula- 

 Zone ; this sequence exhibits an abundant and characteristic 

 coral- and brachiopod-fauna, and is well-defined as the 

 Syringothyris-Zone. 



