THE AVONIAN OF THE AVON GORGE 
149 
BRACHIOPOD-GENERA. 
(In the descriptions of ]Brachiopod genera which follow, it 
would be impossible to estimate the amount of my indebtedness 
to HalFs classical work on the ‘ Glenera of Palaeozoic Brachio- 
poda.’) 
For figures illustrative of the several genera of Carboniferous 
Brachiopoda, I refer throughout, under the abbreviation ^Dav.\ 
to Davidson’s ‘ Monograph of British Carboniferous Brachio- 
poda/ voL 2. (Pah Soc. 1857-1862). 
Productus. 
Hinge-line straight. 
Pedicle-valve convex, with large incurved beak. 
No area or teeth. 
The much -branched adductor-scars are bisected by a 
mesial ridge. 
The large diductor-scars lie below and outside the adductors. 
Brachial-valve concave. 
No sockets. 
The mesial septum is a strong ridge which terminates at the 
hinge line in the massive cardinal-process. 
The adductors lie one on each side of this ridge. 
Each of the two brachial ridges starts out horizontally 
from the lower corner of an adductor scar and curves round 
like a crook. 
External ornament: 
Close longitudinal ribs, usually crossed by concentric 
wrinkles in the region of the beak. 
Hollow spines projecting from the ribs, especially on the 
shoulders of the valve in the neighbourhood of the 
hinge-fine. 
Figures: Dav. Plates 31 to 44, 
