172 BRITISH AVONIAN CONODONT FAUNAS 
and conspicuously pointed apical denticle. The anterior bar is deeper than the 
posterior, and carries from 4 to 6 denticles on its oral edge. These are very strongly 
laterally compressed and more or less sharply recurved, being confluent for the 
greater part of their length. Their apical halves are discrete, and they are sharply 
pointed with straight anterior and posterior edges, the anterior edge tending to be 
sharply deflected at an angle of about 130° at or near the point of confluence with the 
adjacent denticles, but the posterior edge being straight throughout its length. 
Germ denticles are visible in places on the anterior bar, especially at its junction 
with the apical denticle. The most posterior denticle of the apical bar is so coalesced 
with the anterior edge of the apical denticle that only its highest portion is discrete. 
The anterior bar tends to show a slight increase in depth anteriorly ; the denticles in 
the posterior two thirds of the bar are of more or less uniform height. There may, 
however, be I or 2 much smaller blunt denticles present on the spatulate anterior end. 
The denticles may curve slightly inwardly in some specimens. The inner lateral face 
of the anterior bar is more or less flat, but the outer lateral face has a conspicuous, 
shoulder-like thickening near the base of the denticles. The anterior bar tapers 
sharply towards the aboral margin. 
The apical denticle is at least three times as wide as the largest denticles of the 
anterior and posterior bars. It is very sharply pointed, and is only about twice as 
long as its basal width. It is recurved posteriorly at an angle of about 60° to the 
posterior bar, and germ denticles are conspicuous at its base. There is a feebly 
flaring protrusion of the basal margin below its posterior margin. 
The posterior bar is shorter and shallower than the anterior, and bears up to 9 
denticles of more or less uniform height, basally confluent, but their apices discrete 
and sharply pointed. They tend to be very slightly smaller than those of the larger 
series of the anterior bar. The posterior bar thickens towards its aboral surface, 
which is wide and flat, as an extension of the basal cavity below the apical denticle. 
It decreases in both width and depth posteriorly, however, and its posterior aboral 
margin is bluntly rounded. Its inner lateral face is more or less flat and the posterior 
denticles are gently inclined to the base of the posterior bar. The posterior bar and 
the anterior bar have relatively straight aboral margins and they make an angle of 
about 130° with one another in a vertical plane. 
The whole unit is strongly bowed laterally in a horizontal plane so that it is concave 
on the inner side, and the denticles are also incurved to a varying degree. This is 
especially true of the apical denticle. The anterior edge of the anterior bar has an 
acute angle at the anterior aboral margin and is inclined sharply posteriorly, with a 
faintly serrated anterior edge in some specimens. In outer lateral view the lateral 
faces of the unit are flat to gently convex, and the inner curvature is a conspicuous 
feature. In most specimens there is developed to a varying intensity a bevelled 
aboral margin, especially conspicuous in the median half of the unit, which includes 
the posterior part of the anterior bar and the anterior part of the posterior bar. The 
outer lateral view of the navel below the posterior edge of the apical denticle is 
distinct and forms a rather flattened apical area. 
In aboral and outer lateral views the basal cavity is a conspicuous feature, partic- 
