go BRITISH AVONIAN CONODONT FAUNAS 
REMARKS. The genera Synprioniodina, Euprioniodina and Neoprioniodus have 
essentially the same outline and differ in the presence, or absence, of denticles on the 
anticusp. The genera Synprioniodina and Euprioniodina are here considered 
synonyms and are characterized by a denticulated anticusp. Neoprioniodus is a 
similar pick-shaped form to Euprioniodina, but has no denticulated anticusp. 
As Scott and Collinson (1961) pointed out, there appears to be a number of forms 
intermediate between Euprioniodina and Neoprioniodus. Sannemann (1955), 
Bischoff (1956) and Helms (1959) have assigned all such specimens to the genus 
Prioniodina. However, the specimens they refer to Prioniodina do not closely 
resemble the type species of Prioniodina, Prioniodina subcurvata. A detailed 
revision of the pick-shaped forms is necessary, but as few specimens referable to the 
genus Ewprioniodina have been found in the present faunas, it is impossible to under- 
take this study. 
It is difficult to distinguish Euprioniodina from some species of Apatognathus. 
We have divided the two genera by assigning to A patognathus those species in which 
there is conspicuous lateral flexing of one or both bars. 
Euprioniodina caverna (Collinson & Druce) 
Plate 22, figs. 11a, b 
Synprioniodina caverna Collinson & Druce in press. 
MATERIAL. 14 specimens : figured, X 83. 
Rance. North Crop 3D 14/15. 
DESCRIPTION. The present specimens have a greatly elongated anterior bar, 
which is more or less straight, and which bears a series of at least twelve laterally 
compressed, confluent denticles on its anterior edge. These are small and of uniform 
size, being considerably smaller than any of those on the posterior bar. The apical 
denticle, which is aligned with the main line of the anterior bar, is relatively short ; 
it is sharply pointed, with sharp anterior edges and a gently convex outer lateral face. 
The junction of the anterior and posterior bars is marked by the development of an 
apical lamella, which is depressed and has a flat surface in outer lateral view. The 
posterior bar is straight to feebly convex in outer lateral view and is also flexed 
inwardly. It bears a series of about 14 denticles on its oral edge, which show a broad 
tendency to increase in size posteriorly, though this is not a regular feature. They 
are basally confluent but apically discrete and are elongated and pointed, being at 
least two to three times as long as those of the anterior bar. They are directed 
forward parallel to the apicle denticle and are also curved gently inward. 
In inner lateral view the surface of the posterior bar is gently convex, and that of 
the anterior bar more or less flat. The denticles are distinctly curved inward and 
there is a very sharp aboral flexure below the apical denticle with an angular to 
strongly convex apical lamella. 
The aboral surface is excavated by a narrow groove along the whole of its length, 
this being a continuation of the wide flaring cavity below the apical lamella. 
