BRITISH AVONIAN CONODONT FAUNAS 161 
blade-like anterior denticle, which is enormously elongated in comparison with its 
rather slight aboral process. The latter is only about one-sixth to one-seventh the 
total length of the denticle. The posterior bar is also conspicuous, being short and 
sharply down-curved. The denticles of the posterior bar show a sharp decrease in 
length towards the posterior end of the bar. Those adjacent to the anterior denticle 
tend to be greatly elongated in comparison with those that follow. All are slender, 
with more or less sharp anterior and posterior edges, and gently convex lateral faces. 
They are discrete for about half their length and are regularly pointed. The whole 
unit is more or less strongly curved inwards in a horizontal plane. 
The anterior denticle is greatly elongated and is very slender in its general form, 
being bluntly to sharply pointed at its apical tip. It extends as an aboral process 
only for a short distance, about one-sixth to one-seventh of its total length, below the 
level of the posterior bar. The anterior and posterior edges are generally straight, 
though in a few specimens they may be feebly recurved, and in other specimens there 
is a very slight anterior flexure of the aboral process. The anterior denticle has 
sharp anterior and posterior edges and gently convex lateral faces. It stands erect 
to the anterior portion of the posterior bar. The aboral process is more or less 
sharply pointed and triangular in form, without any conspicuous lateral flaring 
developed on the inner aboral margin. The anterior denticle is slightly curved 
inward in its distal third. The denticles of the posterior bar range from Io to 21 in 
number and show a marked decrease in size posteriorly. The 2 adjacent to the 
anterior denticle are virtually confluent with it, only their apices being discrete. 
The remaining denticles of the posterior bar tend to be smaller and to be inclined 
more sharply posteriorly. They are discrete for about half their total length in 
complete specimens. The posterior bar shows a marked decrease in depth from the 
anterior to the posterior end. The posterior terminus is bluntly rounded. It has 
more or less flat to gently convex lateral faces, and a sharply bevelled aboral margin 
on both the inner and outer lateral faces. The whole unit is recurved inwardly in a 
horizontal plane. There is a relatively inconspicuous cavity below the anterior 
denticle, which extends as a shallow slit along the posterior bar and the antero-aboral 
process. 
REMARKS. Hass (1953 : 88) erected the species Prioniodus singularis to include 
the present specimens. However, because the species was illustrated and described 
by Scott, even as part of a natural assemblage, it seems to us that his name must have 
priority. We, therefore, regard Prioniodus singularis Hass (1953 : 88, Pl. 16, fig. 4) 
as a junior synonym of Scott’s species. 
Neoprioniodus peracutus (Hinde) 
Plate 21, figs. 12a—15b 
1900 Prioniodus peracutus Hinde (partim) : 343, Pl. 10, fig. 22 only. 
1926 Prioniodus peracutus Hinde ; Roundy : 1o, Pl. 4, fig. 6. 
1928 Prioniodus pevacutus Hinde ; Holmes: 21, Pl. 3, fig. 38. 
1953 Prioniodus ligo Hass: 87, Pl. 16, figs. 1-3. 
1957 Neoprioniodus erectus Rexroad : 34, Pl. 2, figs. 23, 25. 
