156 BRITISH AVONIAN CONODONT FAUNAS 
The apical denticle is smaller than the large denticle on the anterior bar but of 
similar general form. Its most conspicuous feature is the very strong, internal lateral 
extension of the aboral portion, to form the inner lateral flange. On the aboral 
margins both the anterior and the posterior bars are more or less straight. Their 
most striking feature in inner lateral view is the development of a longitudinal ridge 
parallel to their bases, which rises higher on the faces towards the apex, and 
represents the bevelled margin of the flattened aboral surface. 
In lateral view this latter feature is less conspicuous and the whole unit is flat to 
feebly convex in general form. 
REMARKS. This species shows appreciable variation. The specimens illustrated 
in Pl. 24, figs. 8, 10 and 11 are closely similar. That of Pl. 24, fig. 9, resembles them 
in overall form but has an additional denticle developed anterior to the main denticle 
of the anterior bar, and the apical and posterior denticles also tend to be more sub- 
circular than those of typical members of the species. Similarly, other specimens 
have two smaller denticles developed anterior to the main denticle of the anterior bar 
and also have more sub-circular denticles. It may be that these specimens should be 
regarded as distinct species but they are provisionally included in Metalonchodina 
bidentata. 
Genus NEOPRIONIODUS Rhodes & Muller 1956 
1956 Neoprioniodus Rhodes & Miller : 698. 
TYPE SPECIES. Pvioniodus conjunctus Gunnell 1931. 
Neoprioniodus antespathatus Collinson & Druce 
Plate 21, figs. Ioa—11b 
Neoprioniodus antespathatus Collinson & Druce (in press). 
MATERIAL. 2 Specimens : figured, X 257, X 258. 
RANGE. North Crop 3D 8-3D 16. 
DescripTIon. This is a neoprioniodid with a slender anteriorly directed anterior 
denticle, with sharp anterior edge, blunt posterior edge, and biconvex outline. The 
posterior bar is slender, decreasing in depth posteriorly, and it has a conspicuously 
concave junction with the aboral process. Its oral surface bears a series of about 9 
denticles, the largest of which are in the anterior half, and which show a broad 
tendency to decrease in size posteriorly, though this tendency is not conspicuous or 
regular. The denticles are basally confluent, but are discrete for most of their 
length. They are of slender general form, with sharp anterior and posterior edges 
