﻿194 DK. A. VATJGHAN ON THE PAL^ONTOLOGICAL [May I905, 



Special fa unal characters : — 

 Brachiopods : 



Orthotetes erenistria, mut. C, and Chonetes aff. papillonacea 

 crowd the beds at certain levels (often the Chonetes passes into a 

 strongly-convex variant, Cli. cf. comoides). 



Syringothyris cusjoidata and Productus aff. semireticulatus are 

 met with occasionally. 



Syringothyris aff. laminosa, though never actuary abundant, 

 can always be found, and is highly characteristic of the zone. 



Corals : 



Syringopora cf. reticulata occurs. 



Miehelinia megastoma is not uncommon. 



Amplexus probably occurs here. 



Za/phrentis is seldom found, except at the base (in Horizon y). 



Caninia cylindrica attains its maximum at the base. 



Note. — In the Avon section the uppermost beds of this zone are unfossiliferous, 

 so that there appears to be a remarkable palaeontologisal break between this 

 zone and the succeeding Seminula-Zone ; this break is, however, partly filled in 

 by certain beds found in neighbouring parts of the Bristol area (see under 

 Failand and Clevedon). I shall consequently defer the necessary discussion, 

 as to the advisability of retaining a single zone (the Caninia-Zone) to cover 

 both the zone C and the subzone S 1? until a later portion of the paper (p. 260). 



Visean or Upper Carboniferous Limestone. 

 S = Zone of Seminula ficoidea and its allies (Seminula-Zoug) . 



Lithological and paheontological details are more conveniently 

 set out under the separate subzones. 



The essential faunal characters of this zone are the extreme 

 abundance and the association of Seminula spp., Lithostrotion 

 Martini (vars. & muts.j, and giganteid Producti (including Productus 

 aff. Cora). 



The lower subzone (S T ) is distinguished by the survival of 

 Tournaisian forms, such as Syringothyris spp., Productus aff. 

 semireticulatus, Caninia aff. cylindrica. The upper subzone (S 2 ), 

 on the other hand, is characterized by the incoming of forms which 

 abound in the Dibuno<p7iyllum-Zone, such as Clisiophyllids, Cyatho- 

 ■jyhyllum Murchisoni, Alveolites. 



Subdivisions : — 



Sj = Subzone of Productus semireticulatus, mut. Sj = 

 Upper CANiNiA-Zione. 



Lithological character: 



(1) Shales and thick bands of dolomite and occasional beds of 



oolite. Succeeded by 



(2) Massive limestones with thin shale-partings ; many of these 



limestones are appreciably dolomitic, and are beautifully 



