158 
THE AVONIAN OF THE AVON GORGE 
The surface is either smooth, or divided by a small number 
of radial grooves into broad flattened ‘ ribs.’ 
No dental plates and consequently, in the cast, the sides of 
the beak are rounded. 
The thin outermost shell-layer is strongly punctate (a fact 
which accounts for the ghstening surface). 
The internal surface of the valves has deep, narrow radial 
grooves which diverge from the beak, and consequently 
the cast has corresponding sharp, septum-like ridges. 
The essential characters are the smooth exterior, the short 
hinge-hne, the punctate outer layer and the absence of 
dental plates. 
Figures: Dav, Plates 9, 11 and 12. 
Ueticularia. 
This genus is here retained, tentatively, to include all those 
Spiriferids whose external ornament consists of concentric 
rows of adpressed, hollow radial spines ; the general form 
agrees with that of Martinia. 
It is however very doubtful whether all the forms which 
come under this general definition are correctly grouped to- 
gether in a single genus. 
The genotype is Sf infer imhricatus (Sow) which has strong 
dental plates in the pedicle valve and an external ornament 
composed of double barrelled (nostril-hke) spines (see 
figure above). 
