24 THE CARBONIFEROUS LIMESTONE OF BURRINGTON COMBE 
in the Cleistopora Zone. The top beds of the Cleistopora 
Zone, however, contain nearly all the brachiopods charac- 
teristic of Horizon /3 ; and the failure to distinguish this 
horizon is very probably due to the absence of satisfactory 
exposures. 
Subdivisions. 
(i) Clathratus sub-zone. 
Special faunal characters. 
Brachiopods. 
Clioihyris Royssii (mut /3) is not uncommon at the 
base of the sub-zone. 
Cliothyris glahristria occurs throughout and gradually 
increases in abundance. 
Spirifer ah. clathratus and var. are extremely abundant 
throughout this sub-zone. 
Syringothyris aff. cuspidata, Leptaena analoga and Pro- 
ductus cf. Martini are abundant in the lower part of the 
sub-zone. 
Orthetetes aff. crenistria is abundant throughout. 
Chonetes cf. hardrensis reaches a maximum near the 
base of this sub-zone, where it is extremely abundant ; 
it continues abundantly throughout ; and near the top 
it is for the first time associated with a mutation towards 
Chonetes aff. papilionacea. 
Rhipidomella aff. Michelini occurs throughout and reaches 
a maximum at the top of the sub-zone. 
Reticularia aff. lineata is not infrequent. 
A single interesting Productus of the type of P. Cora 
has been found in this sub -zone. 
Corals. 
Zaphrentis aff. Phillipsi enters at the base of the sub- 
zone and immediately becomes fairly common. 
Michelinia cf. favosa enters at the base and gradually 
increases in abundance. 
