Vol. 62.] LIMESTONE OP THE MENDIP AREA. 327 



Very characteristic features of this phase are the common occur- 

 rence of Modioliform lamellibranchs and the great abundance of 

 ostracods at recurring levels. The brachiopod-fauna includes 

 Chonetes cf. liardrensis (abundant), Ch. cf. crassistria, Athyris 

 Royssii (common), Orthothetes aff. crenistria, Spirifer aff. clathratus, 

 Camarotoechia aff. mitcheldeanensis, and (Discina) sp. Better ophon sp. 

 occurs abundantly. 



Although the development of this phase at the base of the Avonian 

 sequence constitutes a persistent and important feature, yet. the 

 faunal characters of the series do not justify its separation as a 

 distinct zone, and it must, therefore, be regarded as the initial, 

 shallow-water phase of the Cleistopora-Zone. 



At the top of the series occur characteristic red limestones, mainly 

 composed of crinoid-debris, but containing abundant Rhabdomeson. 

 (The 'Bryozoa-Beds.') 



K x = Subzone of Productus bassus. (jb^szjs- subzone.) 



This forms the lowest portion of the main zone, and is charac- 

 terized by the great abundance of: — 



Camarotoechia mitcheldeanensis, Orihoihetes aff. crenistria, mut. K x , 

 Productus bassus, and Chonetes ' Buchiana.' 



Chonetes cf. liardrensis occurs abundantly. 



Eumetria aff. carbonaria occurs not uncommonly, and is, 

 apparently, confined to this subzone. 



Athyris Royssii, Reticularia cf. reticidata, Rhipidomella aff. 

 Micheiini, Syringothyris aff. cuspidata, mut. K, and Spirifer aff. 

 clathratus range throughout, and the latter fossil becomes abundant 

 at the top of the subzone. 



Productus cf. Martini occurs sparingly in the uppermost beds. 



The gasteropod Capulus cf. incequalis is abundant in the lower 

 beds. Bryozoans (Rhabdomeson) are abundant. 



K 2 = Subzone of Spiriferina cf. octoplicata. (octoplicata- 

 subzone.) 



This includes the uppermost portion of the zone, as well as the 

 horizon of overlap with the Zaphrentis-Zone (Horizon (3). 

 The special features of this subzone are : — 



(1) The occurrence of Spiriferina cf. octoplicata, which attains its maximum 



at the top, and has not been recorded outside the subzone. 



(2) The increasing abundance of Spirifer aff clathratus and var., Productus 



cf. Martini, Rhipidomella aff. Micheiini, and Chonetes cf. harclrensis. 



(3) The common occurrence of Athyris ( Actinoconchus) cf. lamellosa. 



Orthothetes aff. crenistria, which shows a mutational change, is 

 extremely abundant throughout. 



Syringothyris aff. cuspidata, mut. K, attains its maximum in the 

 lowest part of this subzone, and persists abundantly throughout. 



Reticularia cf. reticulata and Athyris Royssii occur commonly 

 throughout. 



