THE AVONIAN OF THE AVON GORGE 
157 
The Spiriferids include all Brachiopods which exhibit the 
following characters : — 
(1) Straight hinge hne. 
(2) An area with central delthyrium. 
(3) A pair of internal ‘ spires ’ whose apices are directed 
towards the sides. 
(4) The apex of the beak unperforated. 
Spirifer. 
This genus is employed in this paper to denote those carboni- 
ferous Spiriferids which possess : — 
(1) A well-developed area. 
(2) A pointed beak, curved over the area, 
(3) Mesial fold and sinus, 
(4) Strongly marked radial ribbing over fold and sinus as 
well as over ':he flanks. 
The hinge-line is usually the widest part of the shell, as for 
example in the groups of Sp. striatus and Sp. bisulcatus. 
Figures: Dav. Plates 2 and 6. 
But, in certain species, the hinge line is shorter than the 
greatest width, for example in Spirifer planicosta (see Dav. 
PI. 6, fig. 20). 
strong ridges 
Martinia : pedicle valve (cast). 
This genus includes the groups of Spirifer glaber and Spirifei 
ovalis. 
Form oval (either transverse or elongate). 
Hinge-hne short and the area small and triangular 
