154 BRITISH AVONIAN CONODONT FAUNAS 
anterior inner lateral edge of the unit. There is a narrow V-shaped trough developed 
adjacent to the blade, running towards the posterior end of the unit on the outer 
margin of the carina, and becoming shallower and narrower posteriorly. In outer 
lateral view the blade is conspicuously deeper than the platform. It is of regular 
depth throughout its length and in some specimens shows a tendency to increase 
anteriorly in depth. It is very bluntly rounded antero-aborally, and is strongly 
down-flexed in relation to the blade. Although the junction between the two is 
curved, the anterior aboral edge of the blade makes an angle of about 45° with the 
aboral edge of the posterior platform. The oral surface of the blade bears 6 or 7 
fused denticles, the apical tips of which are discrete and bluntly rounded. 
In outer lateral view the posterior platform has a bluntly serrated surface and its 
outer lateral face slopes down sharply towards the median aboral keel. The 
posterior end is more or less flat, and the denticles of the posterior median carina tend 
to be higher in outer lateral view than those on the edge of the platform. The 
posterior third of the platform is straight, but the anterior part is gently concave. 
The denticles of the anterior blade are more or less uniform in height, although the 
most posterior tends in some specimens to be rather larger than the rest. They are 
more or less erect, though the most posterior denticle may be slightly inclined 
posteriorly. 
In inner lateral view the aboral surface of the whole unit appears to be gently 
convex, except for the rather straight posterior termination. The oral edge is more 
or less conspicuously serrated by low nodose confluent nodes, and the anterior inner 
edge is frequently developed into one or two rather conspicuous denticles, its antero- 
aboral margin being bluntly pointed and making a very prominent bifid junction with 
the anterior blade. The extension of the posterior carina is a prominent feature in 
this inner lateral view. The inner oral margin of the platform is strongly convex, 
but it flattens off along the mid-height of the unit, and the lower part is flat to 
strongly concave, sloping rapidly towards the elongated aboral keel. 
In aboral view there is a prominent, but very small, median pit with inconspicuous 
edges, which is developed near the junction of the blade of the platform. It is 
biconvex in outline and is elongated antero-posteriorly. A shallow rather flat aboral 
surface extends posteriorly from it along the unit with an inconspicuous median slit 
developed towards the posterior end. Anteriorly a thin slit runs towards the 
junction of the inner anterior edge with the anterior blade. 
The posterior end of the platform is marked by a more or less vertical face, with 
rounded posterior aboral margin. The platform deepens towards the anterior inner 
edge when seen in inner lateral view, and this is a conspicuous feature of the unit. 
Genus METALONCHODINA Branson & Mehl 1941 
TYPE SPECIES. Prioniodus bidentatus Gunnell 1931. 
Metalonchodina bidentata (Gunnell) 
Plate 24, figs. 8a-11b 
1900 Polygnathus convexus Hinde (partim) : 342, Pl. 9, fig. 8. 
