242 BRITISH AVONIAN CONODONT FAUNAS 
RANGE. Avon Gorge S 45-S 58. 
DescripTion. The distinctive feature of this species is its general elongate form 
and its median anterior blade. This is continued posteriorly for a short distance on 
the platform as a short carina. The median trough is narrow but deep, and the 
whole platform is conspicuously lanceolate in oral view, with straight or only gently 
convex lateral margins and a conspicuously pointed posterior end. The posterior 
median part of the platform bears a nodose to sharp, short carina, which extends only 
a short distance onto the platform beyond the posterior end, but is also extended 
posteriorly beyond the termination of the platform proper. The blade tends to be 
rather long, with fused denticles. The platform is smooth and V-shaped, and rela- 
tively deep in relation to its width. It has regularly and bluntly crenulate lateral 
margins and the whole platform tends to decrease in width aborally,so that theaboral 
edge at the posterior end is more or less sharp. There is an elongated aboral cavity 
below the anterior third of the platform which is shallow and flaring and more or less 
symmetrical. It is extended anteriorly and posteriorly as a thin, slit-like excavation. 
The anterior blade is deeper than the adjacent part of the posterior platform and 
the denticles are bluntly tipped and coalesced. 
The present specimens show some variation in the degree of posterior constriction, 
in the development of the posterior carina, and in the form of denticulation of the 
anterior bar. 
REMARKS. Rexroad & Collinson (1963 : 20) have shown that the genus Taphro- 
gnathus and the genus Cavusgnathus are closely related and that in some faunas 
transitional forms between these two genera can be seen. In our faunas transitional 
forms are also found (PI. 13, figs. 1-3c). The medial blade of Taphrognathus appears 
to move to take up an outer lateral position. However, since the blade is not 
completely lateral, it is difficult to determine whether these specimens belong to the 
genus Taphrognathus or to the genus Cavusgnathus. We have followed Rexroad & 
Collinson in placing them as transitional species between the two genera. They can 
be seen to be transitional, not only in the form of the anterior blade, but also in the 
general outline of the cavity, and in the reduction of the posterior carina. 
Gen. nov. A sp. 
Plate 25, figs. 6a, b 
MATERIAL. I specimen : figured, X 409. 
LOCALITY AND HORIZON. North Crop. Sample ZLA 6. 
Rance. North Crop ZLA 6. 
DeEscrIPTION. The unit is of a hibbardellid type, but the anterior arch is 
separated from the apical denticle by a short, denticulate, anterior bar. The anterior 
arch is broken, but can be seen to be denticulate. The apical denticle is massive, sub- 
circular in cross-section and is curved posteriorly. The posterior bar is thin and 
finely denticulate. 
In aboral view the unit is excavated, the basal cavity running from the apical 
