BRITISH AVONIAN CONODONT FAUNAS 99 . 
figs. 11, 12). The blade is generally highest at its anterior end, although the two 
most anterior denticles may be relatively small ; the posterior end of the unit tends 
to be lower. The blade has a bluntly spatulate to rectangular anterior end and a 
more or less straight or very feebly convex aboral edge. The denticles are fused to 
about mid-height but their apices are discrete. 
The carina consists of low, fused denticles, of about equal height to those at the 
posterior portion of the anterior blade. The carina is depressed in the posterior half 
of the platform, and the level of the denticles tends to be relatively higher than those 
of the lateral ornament, which reaches about two thirds of the total depth of the 
posterior platform from the top of the carina. The posterior platform itself is 
characterized by a variably asymmetrical basal outline. In some specimens the 
basal outline is almost biconvex, but in most the outer aboral margin is more con- 
spicuously flared than the inner ; in a few individuals it is so strongly flared that it 
gives to the basal outline a form reminiscent of such species as G. bilineatus or G. 
semiglaber (e.g. Pl. 17, fig. 12a). In spite of this, the platform ornament remains 
distinctive ; the ornament on the inner lateral surface of the platform extends 
further forward than that on the outer, and consists of a low series of fused nodes, 
running sub-parallel to the carina but converging with it in the posterior platform, 
and looping round the posterior end of the carina to give a bluntly rounded, pointed 
outline (e.g. cf. Pl. 17, figs. 11b, 12b). The outer platform ornament tends to be less 
conspicuous than that of the inner; the lateral ridges, which characterize the 
denticles of the inner platform, are absent from the outer platform. 
The basal cavity is flaring and asymmetrical, being deepest in the anterior third of 
the platform and continuing for a variable distance below the posterior portion of 
the anterior blade. 
REMARKS. In some individuals (e.g. Pl 17, fig. rob) the posterior carina tends to 
continue somewhat beyond the level of the lateral denticles, which then tend to merge 
with it anterior to the termination of the platform. In this they approach other 
subspecies of the genus but are otherwise distinguishable from them. 
Gnathodus girtyi collinsoni subsp. nov. 
Plate 16, figs. 5a—-8d 
1962 Gnathodus givtyi Form C Meischner : 31, fig. Io. 
1963 Gnathodus girtyi B Hass ; Bouckaert & Higgins: 17. 
1965 Gnathodus roundyi Gunnell ; Murray & Chronic (partim) : 598, Pl. 71, figs. 5, 6 only. 
DERIVATION OF NAME. After Dr. Charles W. Collinson. 
Dracnosis. Subspecies of Gnathodus girtyi in which lateral denticulation of 
platform is confined to inner lateral side. Very feeble nodes may sometimes be 
developed on outer lateral platform. 
MATERIAL. 13 specimens : Holotype X 99, Paratypes X 100, X ror, X 102 (all 
figured). 
TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. 
