BRITISH AVONIAN CONODONT FAUNAS 187 
Polygnathus inornatus rostratus subsp. nov. 
Plate 10, figs. 7a—gc 
? 1939 ©Polygnathus ivvegularvis Cooper : 400, Pl. 39, figs. 57, 58. 
1962 Pseudopolygnathus ? cf. Pseudopolygnathus triangula Voges ; Miller: 1388, text-figs. 
ga-c. 
DERIVATION OF NAME. From the development of a rostral ridge on the inner 
platform. 
Diacnosis. P. inornatus possessing rostral or pseudorostral ridge on inner 
platform. 
MATERIAL. 28 specimens : Holotype X 530, Paratypes X 356, X 357 (all 
figured). 
TYPE LOCALITY AND HORIZON. North Crop. Sample KL 4. 
RANGE. North Crop KL 4-KL 16-KL 20, ZL 1, Avon Gorge K 12-K 14. 
DESCRIPTION. Specimens of P. inornatus rostratus agree closely with specimens 
of P. inornatus s.s., apart from the configuration of the inner margin. There is a 
tendency for the anterior part of the inner margin to move towards the anterior 
blade, the posterior part then becoming lobate. The anterior inner margin tends to 
run towards the carina for a very short distance in more advanced forms. 
In some cases there tends to be a thickening of the aboral portion of the platform 
wall, so that in oral view the platform edge does not form the inner edge of the unit. 
REMARKS. This subspecies includes all specimens showing a breakdown in the 
smoothness of the inner edge. Thus in more advanced forms a pseudo-rostral ridge 
can be seen (e.g. Pl. 10, fig. 7b). In less advanced forms there may be thickening of 
the aboral edge and a breakdown of the curvature of the inner edge (e.g. Pl. 10, 
fig. gb). The strength of development of the ridge bears some relationship to both 
ontogeny and to stratigraphic position. This involves an offset, tilt and deflection 
towards the carina of the inner lateral margin, the pseudo-rostral ridge having a 
sharp and well-defined outer face. The posterior portion of the zidge, which runs 
sub-parallel to the carina, is conspicuously higher than the adjacent inner margin, 
although the posterior termination is low and indistinct. 
Polygnathus inornatus vexatus subsp. nov. 
Plate 10, figs. Ia—3c 
DERIVATION OF NAME. From the troublesome problem of specific assignment. 
DiaGnosis. Subspecies of P. inorvnatus. An arched unit with symmetrical 
platform, curved axis, and fairly long blade, composed of broad, fused, chevron- 
tipped denticles. Carina low, nodose, extending beyond platform as short posterior 
blade. Symmetrical lanceolate platform, ornamented with medium to strong 
transverse ribs ; platform edges serrated. Basal cavity small, occurring near 
junction of blade and platform. 
MATERIAL. 5 specimens : Holotype X 358, Paratypes X 359, X 551 (all figured). 
