BRITISH AVONIAN CONODONT FAUNAS 165 
The anterior denticle is elongated, wide and bluntly pointed. It is gently recurved 
in its distal half, but its proximal half stands only slightly inclined to the anterior 
portion of the posterior bar. It has sharp anterior and posterior edges and very 
feebly convex lateral faces, the outer distal lateral face being almost flat. 
The aboral process is broad in relation to its length. Its anterior edge is a con- 
tinuation of the anterior edge of the anterior denticle, and it is more or less straight. 
Its anterior aboral termination is bluntly rounded and its posterior aboral edge is 
strongly convex. It has flat lateral faces. 
The posterior bar is elongated, and has a concave proximal portion and a relatively 
straight distal portion when seen in outer lateral view. It decreases in depth 
posteriorly and bears about 15 denticles ; those of the median third tend to be the 
largest and they decrease posteriorly in size ; they are basally confluent but are 
discrete for most of their length, with sharp anterior and posterior edges and gently 
convex lateral faces. There is a tendency in the median part of the bar for a 
hindeodellid type of denticulation, but this is not a conspicuous feature of the unit. 
The outer lateral face of the posterior bar is flat and shows a very slight bevelled 
ridge parallel to its aboral surface. The whole unit is gently incurved in a horizontal 
plane, so that its inner lateral face is concave. The denticles of the posterior bar 
stand more or less erect to the bar itself. 
In inner lateral view the anterior denticle is much more strongly curved and the 
curvature is especially strongly developed on the posterior proximal lateral face. 
The inner aboral longitudinal edge of both the aboral process and the posterior bar 
are sharply bevelled and the inner lateral curvature of both the anterior denticle and 
the posterior bar are conspicuous. 
The aboral surface is marked by a shallow pit below the anterior denticle, which is 
extended posteriorly as a very narrow slit-like cavity. The basal cavity also extends 
anteriorly as a narrow slit-like process, running along the median part of the anterior 
aboral surface. The basal cavity itself is not conspicuously laterally expanded. 
There is a strong bevelled flange on the inner aboral edge of the anterior aboral 
process. The strongest lateral curvature of the posterior bar occurs in its anterior 
half, the posterior part being more or less straight. 
Remarks. The only substantial difference between the present species and NV. 
scitulus (Branson & Mehl) is the longer posterior bar of the present specimens, which 
bears a greater number of denticles. There seems to be a morphological discon- 
tinuity between the two, but we are not certain about this and further study may 
indicate that the two are morphologically continuous and that N. scitulus should be 
regarded as a junior synonym of N. tulensis. 
Neoprioniodus varians (Branson & Mehl) 
Plate 21, figs. 18a, b 
1940 Prioniodus varians Branson & Mehl : 174, Pl. 5, figs. 7, 8. 
1941 Prioniodus barbatus Branson & Mehl ; Ellison & Graves : 3, 4, Pl. 1, fig. 27 only. 
1957 Prioniodina varians (Branson & Mehl) Bischoff : 49, Pl. 5, fig. 35. 
1957 Prioniodina varians (Branson & Mehl) Ziegler im Fliigel & Ziegler : 50. 
