Vol. 62.] LIMESTONE OF THE MENDIP AREA. 329 



only the occurrence of Spiriferina cf. octoplicata, are precisely those 

 of the lower part of the Zaphrentis-Zone, it is better regarded as the 

 base of that zone than as the top of the Cleistopora-Zowe. 



Z x = Subzone of Spirifer aff. clathratus. (clathratus- 

 subzone.) 



Special faunal characters: — 



Corals : 



Zaphrentis aff. Phillipsi occurs commonly in the lower part. 

 Michelinia cf. favosa enters at Horizon /3, and is abundant at 

 certain levels. 



Syringopora d occurs rarely in the uppermost beds. 



Brachiopods : 



Spirifer aff. clathratus and var. are enormously abundant at re- 

 curring levels throughout. 



Chonetes cf. hardrensis, in the mutation characteristic of the 

 Oleistopora-Zone and this subzone, Productus cf. Martini, Rhipido- 

 mella aff. Michelini, and Reticularia cf. reticulata attain their maxima. 



Orthothetes aff. crenistria, in a characteristic mutation, is enor- 

 mously abundant at certain levels. 



Athyris Royssii, mut. /3, occurs at the base of this subzone, but 

 is not abundant. A. cf. glabristria, mut. Z,, and Syringothyris air. 

 cuspidata, mut. K, are abundant. Leptcena analoga is abundant at 

 certain levels, and attains a maximum. 



Productus aff. pustulosis occurs commonly. Productus aff. Cora, 

 mut., occurs very rarely. 



CamarotoecJiia mitcheldeanensis is comparatively rare above 

 Horizon /3. Syringothyris aff. laminosa is rare. Chonetes cf. 

 papilionacea enters sparingly in the upper part of the subzone. 



Z 2 = Subzone of Zaphrentis aff. cornucopia. 

 (coRNUcopi&sxibzone.) 



This forms the upper half of the zone, and includes the horizon of 

 overlap with the Syringothyris-ZoriQ (Horizon y). 



Special faunal characters: — 



Corals : 



The most important feature of this subzone is the great abundance 

 of Zaphrentis aff. cornucopias and Z. aff. Phillipsi, both of which 

 attain their maxima in the upper part. 



Caninia cylindrica enters early in the subzone, and soon becomes 

 fairly abundant ; it attains a maximum at Horizon y, where it is 

 extraordinarily abundant. 



