150 BRITISH AVONIAN CONODONT FAUNAS 
between the planes of the two bars. The anterior bar is lateral and deflected, bearing 
3 isolated denticles. The posterior bar bears 3 large, posteriorly inclined denticles. 
Genus MESTOGNATAHUS Bischoff 1957 
1957 Mestognathus Bischoff : 36. 
TYPE SPECIES. Mestognathus beckmanni Bischoff 1957. 
DiaGnosis. A canoe-shaped form, with a well-developed platform, tapering to 
anterior and posterior. The platform ornamented by numerous transverse ridges. 
A high anterior blade developed on the outer side of the platform ; inner side of the 
platform, in lateral view, extends further to the anterior, than the outer side of the 
platform, because of the development of the anterior blade on the latter. A deep 
trough runs along mid-length of oral surface. Aborally a small narrow basal cavity 
present. 
Remarks. The genus Mestognathus Bischoff closely resembles Cavusgnathus 
Harris & Hollingsworth, but differs from the latter genus in that it has a small 
narrow basal cavity compared with the wide flaring basal cavity typical of Cavus- 
gnathus. Mestognathus has not been recorded from North America and makes its 
first appearance in Europe in Cu II 6/y. In North America Cavusgnathus makes its 
first appearance at nearly the same horizon and so the two genera may be closely 
related. 
Mestognathus beckmanni Bischoff 
Plate 15, figs. 7a-d 
1957 Mestognathus beckmanmi Bischoff : 37, Pl. 2, figs. 4a, b, c, d, 5, 6, 8, 9. 
1960 Mestognathus beckmanni Bischoff ; Kronberg, Pilger, Scherp & Ziegler: 14, Pl. 3, 
figs. Ia, b. 
1962 Mestognathus beckmanni Bischoff ; Meischner : text-fig. ro. 
1962 Mestognathus beckmanmi Bischoff ; Bartenstein & Bischoff : Tab. 3. 
MATERIAL. 36 specimens : figured, X 245. 
Rance. North Crop CYD 7, Avon Gorge C 15—D 26. 
DESCRIPTION. The carina is restricted to the posterior part of the platform in this 
species, but may in some cases be extended anteriorly to meet the inner lateral face 
at a narrow angle. The anterior blade is high and has from 6 to 12 denticles which 
occupy the anterior margin of the outer side of the platform. The medial trough is 
deep and very wide, and runs for at least half the length of the platform, being 
deepest anteriorly. The unit is about four times as long as it is wide, being widest 
at about mid-length of the platform. In outer lateral view the highest part of the 
anterior blade is about twice the depth of the posterior platform at mid-point. The 
anterior blade is characterized in lateral view by the development of from 6 to 12 
denticles which are basally fused, only their tips being discrete. They tend to be of 
variable size and to have bluntly rounded apices with gently convex lateral faces. 
The largest denticles are the posterior one or two on the blade, especially the most 
