BRITISH AVONIAN CONODONT FAUNAS 233 
Spathognathodus cf. campbelli Rexroad 
Plate 8, figs. Ia—4c 
1957 Spathognathodus campbelli Rexroad : 37, Pl. 3, figs. 13-15. 
1960 Spathognathodus pusillus Clarke : 20-21, Pl. 3, figs. 10, 11. 
1965 Spathognathodus cf. campbelli Rexroad ; Rexroad & Nicoll: 26, Pl. 1, fig. 6. 
MATERIAL. II specimens : figured, X 450, X 451, X 452, X 435. 
RANGE. North Crop CYD 6-3D 19. 
DEscRIPTION. The most distinctive features of the present specimens are the 
deep and relatively short blade, which is almost as deep as the longest oral denticles ; 
the series of up to 20 laterally compressed denticles of which the largest occurs at 
about mid-length ; the marked flaring of the basal cavity, which is confined to the 
posterior half of the unit ; and the gentle posterior deflection in a vertical plane of 
the posterior half of the unit. In lateral view the oral margin is sharply denticulated, 
tending to be straight and rather sloping in the anterior half, and more or less convex 
in the posterior half. There are 17 to 20 denticles on the oral edge of the blade. 
These show a rough increase in size from the anterior denticle to the denticle at about 
mid-length of the blade, which is the largest of the whole blade and is feebly inclined 
posteriorly to the basal surface of the blade. The other denticles of the anterior part 
of the blade are more or less erect and are confluent for most of their length, although 
their apical portions are discrete and pointed. The denticles of the posterior part of 
the blade are all inclined posteriorly. They are discrete for a greater part of their 
length than those of the anterior part of the blade, and the degree of posterior 
inclination tends to increase towards the posterior end of the blade. Those in the 
posterior quarter of the blade tend to be the smallest. The posterior blade decreases 
in depth posteriorly and the posterior end is shallow and bluntly spatulate. It is 
also conspicuously depressed in a vertical plane towards the posterior end. The 
other striking feature in lateral view is the widely flaring and elongate basal cavity, 
the anterior end of which is aligned with the anterior edge of the largest denticle. 
In aboral view the cavity has a strongly biconvex outline and is extended virtually 
to the posterior end of the blade. It is continued anteriorly to the anterior edge of 
the main denticle as a very inconspicuous and narrow slit. 
REMARKS. The present specimens differ somewhat from those described by 
Rexroad in having a rather conspicuously developed denticle at about mid-length. 
In other respects the specimens are closely similar, especially in the general form of 
the basal cavity, which tends to be more rounded anteriorly than it is posteriorly, and 
to have its deepest point near the anterior end. The longitudinal line immediately 
above the level of the navel, which marks the thin basal edges of the unit, is well seen 
under certain conditions of lighting. 
Spathognathodus cf. cristulus Youngquist & Miller 
Plate 8, figs. 7a-8c, 12a-13b 
1938 Spathognathodus regularis Branson & Mehl (partim) : 137, Pl. 34, fig. 2 only (non PI. 34, 
figs. 1, 3, 10 = S. vegularis). 
