Vol. 62.~\ LIMESTONE OF THE MENDIP AREA. 359 1 



never contains Syringothyris aff. mspidata, and would constitute a 

 very broad and ill-defined ' horizon ' of i'aunal overlap. 



In the absence of any satisfactory horizon of overlap, it becomes 

 necessary to fix some arbitrary but satisfactory line of separation. 

 Seminula Jlcoides is not common in the lowest part of S, and is, 

 therefore, of little value for determining the base of that zone. But 

 Lithostvotion Martini, as a dominant form, is characteristic of the 

 whole Seminula-Zone, while it has never been found in association 

 with Syringothyris aff. ciispidata. The base of the Seminula- 

 Zone is, therefore, best defined by the horizon of first 

 occurrence of Litliostrotion Martini. 



It may be mentioned again here, that the base of the Seminula- 

 Zone (as defined by the first occurrence of Litliostrotion Martini) is 

 sometimes marked, in the Hendip area, by the great abundance of 

 that fossil, which is associated with a highly-characteristic fauna. 

 The characteristic members of this fauna are Carcinophyllum men- 

 dij)ense, Camarophoria isorhyncJia, Spirifer cf.furcatus, and Athyris 

 cf. glabristria, mut. S x . Unfortunately, this faunal assemblage is, 

 apparently, localized in its distribution. 1 



Note on the Distinctness of the Clevedonian and 

 Kidwellian Faunas in the Mendip Sequence. 



The following genera of corals are confined to the Cleve- 

 donian : — 



Cleistopora, Michelinia, Zaphrentis, Amplexus. 2 



The following brachiopod-groups are confined to the Cleve- 

 donian : — 



Athyris cf. lamellosa. 

 Eeticularia cf. reticidata? 

 Spirifer aff. clathratus. 

 Spiriferina cf. octoplicata. 

 Syringothyris aff. cuspidata. 

 Syringothyris aff. laminosa. 

 Eumetria aff. carbonaria. 

 Camarotcechia mitcheldeanensis. 



Lepfcsna analoga. 

 Schizophoria aff. resupinata. 

 Productus bassus. 

 Productus cf. Martini. 

 Chonetes ' Buchiana.' 

 Chonctes cf. crassistria. 

 Chonetes cf. hard ren sis. 



The following coral-groups are confined to the Kidwellian :- 



Alveolites septosa. 



Lithostrotion* 



Cyathophyllum Murchisoni (type). 



The great group of the Clisio- 

 phyilids 4 (including Lonsdalia). 



The following brachiopod-groups are confined to the Kid- 

 wellian : — 



Productus scabriculus. Athyris cf. planosidcata. 



The great group of the giganteid Producti is essentially charac- 



1 See footnote, p. 357. 



2 Possibly ranges into the base of the Kidwellian. 



3 Occurs very rarely in the base of the Kidwellian. 



4 Very few early forms occur in C. 



