BRITISH AVONIAN CONODONT FAUNAS 201 
our upper two forms are part of the same phylogeny and should be referred to 
Branson’s species, whereas the homoeomorphic Lower K Zone forms are of distinct 
origin and are best regarded as new species. 
AFFINITIES 
Hass and others have considered that Macropolygnathus Cooper, 1939 is a junior 
subjective synonym of Polygnathus Hinde, 1879. The basal cavity of Macropoly- 
gnathus ithus, the type species of Macropolygnathus, is more akin to Pseudopoly- 
gnathus than to Polygnathus, and transitional forms have been found between M. 
ithus and P. fusiformis. We have, therefore, placed Macropolygnathus in synonomy 
with Pseudopolygnathus. 
Pseudopolygnathus is distinguished from Polygnathus by its laterally expanded 
basal cavity. 
ORIENTATION 
In Pseudopolygnathus primus, the curvature of the longitudinal axis of the cono- 
dont and the shape of the basal cavity are bilaterally symmetrical elements. The 
ornamentation of the platform and a cross section through the blade, near the 
platform, are bilaterally asymmetrical elements. 
The inner side of the conodont is concave and the outer side is convex. Forms are 
designated as right or left, when orientated with the blade placed in front and the 
convex side to the outside. 
Posterior 
True blade 
posterior 
Platform ~ Posterior keel 
Lateral 
nodes i 
Basal cavity 
‘Lips 
Outer side ‘i Trough Anterior keel 
Anterior 
Oral view Aboral view 
Fic. 39. Pseudopolygnathus sp. showing morphological terms used in the text. 
