550 ME. J. A. DOUGLAS ON THE [Nov. I909, 



Z^ Subzone of Spirifer aff. clathratus (clatkratus 



subzone). 



Lithological characters. — Dark-grey and black shales, with 



eccasional bands of crinoidal limestone ; chert-bands rare. 

 Special faunal characters: — 



A densiphylloid Zaphrentis is extremely abundant at the base, 



where it is associated with Productus cf. hurlingtonensis and 



Syringothyris cuspidata in a characteristic mutation. 

 Syringopora 6 is rare ; no other corals have been recorded. 

 Spirifer aff. clathratus and Phipidomclla michelini attain their 



maxima in this subzone. 

 Leptazna andloga, Reticularia cf. reticulata, Athyris lamellosa, and 



Orthotetes crenistria mut. are common at certain levels. 

 Spiriferina cf. octoplicata and Derbya bristolensis are represented 



by single specimens. 



Z 2 = Subzone of Zaphrentis konincki. 

 Lithological characters. — Compact dark-blue and black, 

 thinly-bedded limestones with shaly partings, which become 

 more persistent towards the base. 



The bedding is in places obscured by a strongly developed 

 cleavage. 



Chert is abundant throughout this subzone, and a well-defined 

 cherty band about 40 feet thick forms a noticeable and constant 

 feature at the summit. 

 Special faunal characters: — 



Zaphrentis koninclci enters at the base, and becomes enormously 



abundant at the summit, where it is associated with Caninia 



cornucopice and Campophyllum cylindricum. 

 Michelinia favosa and Syringopora d range throughout. 

 Trilobites and fish-teeth occur frequently in the cherty beds. 

 Syringothyris aff. cuspidata. and Chonetes hardrensis crowd certain 



shaly beds near the base. 

 Orthotetes crenistria, in a characteristic mutation, and Leptcena 



analog a are common. 

 Schizophoria resupinata enters but is never abundant, and 



Syringothyris laminosa is rare. 

 Spirifer aff. clathratus is still common at certain levels. 

 A characteristic piistulose Productus is abundant. 



Horizon y. 



Strictly speaking, there is no horizon of faunal overlap between 

 this and the succeeding zone, for the incoming of the latter is 

 marked by a more or less complete change of fauna, indicating a 

 sudden change of batbymetrical conditions. Since, however, in the 

 top beds of the Zaphrentis Zone, Zaphrentis JconincJci and Campo- 

 phyllum cylindricum occur together in some abundance, a correlation 

 may be made with horizon y of the Bristol area. 



