BRITISH AVONIAN CONODONT FAUNAS 157 
and gently convex lateral faces. They stand more or less erect or gently posteriorly 
inclined in relation to the underlying aboral surface of the bar. The posterior bar is 
gently down-curved, although its distal portion is more or less straight. The aboral 
projection of the anterior denticle is the most massive feature of the unit. It is 
about twice as wide in lateral view as the basal part of the anterior denticle itself. 
Its anterior margin is straight to very gently concave and its anterior aboral termina- 
tion is bluntly pointed. Its posterior aboral margin is very strongly convex and it 
decreases in width towards its distal end. The whole effect is of a massive structure. 
Its lateral faces are more or less flat but the whole unit is feebly curved inwardly. 
In outer lateral view the whole unit is convex, reflecting the inward recurvature. 
In aboral view there is a very inconspicuous cavity developed below the apical 
denticle ; the aboral surfaces of the posterior bar and the aboral process are flat in 
general form, the inner lateral aboral edge being slightly higher than the lower, and 
the whole surface is excavated by a minutely narrow and shallow longitudinal groove. 
The most conspicuous features of this unit are the slender form of the anterior 
denticle and the posterior bar, in contrast to the massive form of the aboral process, 
the whole anterior lateral aboral face of which is more or less concave. 
Anterior denticle 
Anterior edge 
Anterior 
Posterior 
Posterior bar 
Aboral Sd 
process ——— \ # 
Aboral edge 
Fic. 32. Neoprioniodus sp. showing morphological terms used in the text. 
