336 ME. T. E. SIBLY ON THE CAEBON1FEROUS [May I906, 



Variants of Productus hemisphericus are common. Pr. aff. Cora 

 is abundant in a characteristic mutation. Pr. aff. elegans occurs 

 rarely. 



Athyris cf. expansa and Derhya aff. senilis are common. 



Seminula is uncommon. Martini a aff'. lineata, Orthothetes, and 

 Cyrtina are rare. 



D 2 = Subzone of Lonsdalia florijormis. (Lonsdalia- 

 subzone.) 



Special faunal characters: — 

 Corals : 



Lonsdalia floriformis and Litliostrotion Portlocki are highly 

 characteristic. L. irregulare is abundant. Z. Martini, in its muta- 

 tions towards L. irregidare and Z-. Phillipsi, is common. 



Dihunophyllum \\j, Cyclophylhun pacliyendothecum, mut., and 

 £ows<:?«fo'a-like Carcinopliylla are common. 



Oyathophyllum Murchisoni, though far less abundant than in 

 the lower subzone, is still common. 



Koninckophylloid Cyathophylla and a Campophyllid occur in this 

 subzone. 



Syringopora cf. distans is fairly abundant. 



Brachiopods : 



Productus (j> is characteristic and very abundant. Pr. concinnus, 

 mut. D 2 , is characteristic, and occurs very abundantly in the upper 

 beds : costatus-like variants of this form are abundant. 



Productus hemisplierieus is uncommon. Pr. sp., convergent with 

 Pr. margaritaceus, occurs in the upper part of the subzone. Pr. 

 punctato-fimbriatus and Pr. cf. latissimus occur commonly. 



Productus aff. scabricidus is not uncommon. 



Chonetes aff. comoides, in a mutation possessing accentuated 

 Productoid characters, is abundant at certain levels. 



Derhya aff. senilis, Athyris cf. expansa, A. cf. planosulcata, 

 Martinia aff. lineata, Spirifer cf. bisulcatus, and Rhipidomella sp. 

 occur somewhat rarely. 



III. Geneeal Steatigeaphy oe the Caebonifeeous Limestone 



IN THE MENDTP AEEA. 



The following general remarks are intended chiefly to explain 

 the system on which the exposures of the Carboniferous Limestone 

 are classified in this paper. 



Broadly considered, the stratigraphy of the Carboniferous 

 Limestone in the Mendip area has been determined by elevation 

 along four main axes, each of which runs in an easterly and westerly 

 direction. The Carboniferous Limestone of the main Mendip 

 outcrop may, then, be treated with reference to four anticlines 

 which have an easterly and westerly trend ; or rather, more 



