BRITISH AVONIAN CONODONT FAUNAS 101 
and of the basal cavity. The most conspicuous difference is in the character of the 
accessory lateral denticles on the posterior platform. The denticles on the inner 
lateral platform are relatively more strongly developed than those on the outer. 
They consist of up to 9 denticles, the highest and most massive being at the anterior 
end, and are separated by a trough from the main median carina. Those towards the 
posterior end of the series tend to be smaller and also to be developed nearer to the 
carina. The denticles of the outer lateral platform are smaller and fewer in number 
and extend further posteriorly than those on the inner lateral platform. In oral view 
both series of lateral nodes converge posteriorly and fuse with the median carina, the 
carina extending further posteriorly than either series of lateral denticles. In lateral 
view the denticles of the inner series approach the height of those on the median 
carina, but are still fractionally shorter. In outer lateral view the denticles at the 
posterior end of the outer lateral series tend to be slightly larger and more con- 
spicuous than those at the anterior end. The apron on the outer lateral platform, 
when seen in oral view, is relatively much more laterally expanded than that of the 
inner lateral platform. The denticles on the inner lateral platform tend to be 
developed in a semi-transverse form, their outer edges being higher than their inner. 
They show semi-radiate development around the central point of the inner lateral 
platform, but this is not strongly marked in all individuals. 
RemARKS. This subspecies was recognized as a distinct group by Meischner 
(1962) and Bouckaert & Higgins (1963). 
Gnathodus girtyi soniae subsp. nov. 
Plate 17, figs. 5a—8d 
DERIVATION OF NAME. After Miss Sonia J. Kostromin. 
DraGnosis. Subspecies of Gnathodus girtyi resembling G. girty: girtyi in having 
ornamentation developed continuously around posterior platform and encircling 
posterior termination of carina, but differing in development of 1 or 2 low rounded 
inconspicuous nodes on outer-anterior-lateral surface of platform. 
MATERIAL. 18 specimens: Holotype X 113, Paratypes X 115, X 112, X 114 
(all figured). 
TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 12. 
RANGE. North Crop 3D 2-3D 14/15. 
DeEscriPTION. A subspecies of Gnathodus girtyi with greatly expanded apron-like 
posterior platform, the sides sloping sharply down. The median carina is strongly 
developed and its posterior end is completely encircled by the lateral denticles of the 
platform. The inner-lateral parapet is the highest single feature of the platform 
ornament. It begins at a point anterior to the origin of the ornament, on the outer 
lateral side, and has 3 or 4 massive laterally elongate denticles, the highest of which 
tend to be those at the posterior end ; they are separated from the carina by a 
narrow sulcus, which opens anteriorly into a siphonodellid-like spout. The denticles 
decrease posteriorly in size, and are arranged as a linear series of low node-like forms. 
