BRITISH AVONIAN CONODONT FAUNAS 213 
are just higher than the highest point of the platform in lateral view ; the blade is 
made up of 7 to 8 fused, laterally compressed, denticles. 
In aboral view the basal cavity is lanceolate, being widest at the anterior end of the 
platform and narrowing gradually toward the posterior, where it becomes a narrow 
groove in a deep keel. 
REMARKS. It appears that this species is closely related to P. lacinatus, the 
platform ornament serving to distinguish them. 
The most distinctive features of the present species are its more or less laterally 
expanded basal cavity, its relatively strong ornament, and its relatively long blade. 
The platform ranges from elongate pointed to broadly lanceolate in oral outline. 
It is difficult to decide whether this species is better assigned to the genus Pseudo- 
polygnathus or to the genus Polygnathus, but because some specimens possess typical 
pseudopolygnathid cavities, it is here included in this genus. 
Pseudopolygnathus postinodosus sp. nov. 
Plate 6, figs. 6a—c 
DERIVATION OF NAME. After the high denticles of the posterior extension of the 
carina. 
DiaGnosis. Pseudopolygnathus characterized by posterior extension of carina 
bearing a few high denticles. Platform situated in mid-third of unit bears a few 
indistinct nodes confined to convex margins. Anterior blade also distinctive, being 
highest at mid length, sloping abruptly to posterior and more gently to anterior. 
Basal cavity elongate with thickened lips. 
MATERIAL. 3 specimens : Holotype X 496 (figured). 
TYPE LOCALITY AND HORIZON. Avon Gorge Zz Limestones. Sample Z 38. 
RANGE. Avon Gorge Z 13-Z38. 
DEscRIPTION. In oral view the platform is seen to occupy the mid third of the 
unit, the anterior blade the anterior third of the unit, and the posterior extension of 
the carina the posterior third. The axis is straight to slightly curved and it is 
possible to recognize right and left forms, although in the present study only right 
forms have been found. The anterior blade is composed of 7 denticles ; the 3 at the 
posterior are smaller than the other 4. The fourth anterior denticle is highest and 
the third anterior denticle is only slightly lower than the fourth. The anterior two 
denticles are, like the third and fourth, free for the greater part of their length, but 
they are lower than the third and fourth denticles. The carina in the region of the 
platform is low and consists of a number of stubby denticles, which are fused together. 
At the posterior extremity of the platform the denticles of the carina become distinct, 
and on the posterior extension there are a few distinct high denticles. 
In lateral view the denticles of the anterior blade and of the posterior extension of 
the carina are stout and spine-like. The three denticles of the posterior extension of 
the carina are free from the base to the tips, and diverge at a wide angle from one 
another. The anterior edge of the anterior blade and the posterior edge of the 
