104 BRITISH AVONIAN CONODONT FAUNAS 
MATERIAL. 230 specimens : Holotype X 124, Paratypes X 125, X 126 (all 
figured). 
TYPE LOCALITY AND HORIZON. North Crop. Sample 3D 14/15. 
RANGE. North Crop CYD 7-3D 19. 
DescripTION. The blade is generally slightly curved. In lateral view both the 
oral and aboral outlines are nearly straight, although the anterior is slightly higher in 
some specimens. The denticles tend to be larger and more distinct at the anterior 
end and become increasingly small and fused toward the posterior. Most are fused 
to their tips. Both ends of the blade are nearly vertical in most specimens. The 
posterior end of the cup may project beyond the blade. 
In oral view the cup is characteristically sub-quadrangular and slightly asym- 
metrical. The inner half bears a single node which is characteristically large and 
elongate but in some specimens round. The blade is typically more than twice the 
length of the cup. 
REMARKS. This species is very close to G. nodosus. That it is not merely a 
random variant of nodosus, in which one or the other node is undeveloped, is shown 
by the fact that the single node occurs only on the inner side of the cup. 
The present specimens tend to show all the main forms of variation exhibited in the 
platform by G. commutatus. They also show the rectangular profile of the blade of 
that species when seen in lateral view, and also the relative variation in the curvature 
and termination of the carina on the posterior end of the platform. In a very few 
specimens the outline of the platform is more reminiscent of G. symmutatus, but it 
differs from that species in having the square lateral profile of the blade, the oral 
surface being of more or less uniform height, and not showing the pronounced 
decrease in size of the posterior denticles over most of the length of the platform 
(see p. 108). 
In a few specimens the inner platform is more elongate than in typical members of 
the species, the anterior margin being elongated at right angles to the line of the 
blade. These individuals are further distinguished by the presence of two denticles 
on the inner platform developed in a line lying at about 45° to the blade and pointing 
anteriorly, and both being rather laterally compressed and basally confluent but 
with more or less distinct apical tips. These specimens are so close in every other 
respect to those with a single denticle, that there seems no good reason for separating 
them. 
In some specimens the denticle is not fully developed, but is represented by a slight 
swelling occupying the same relative positions on the inner lateral platform, and 
directed at about 45° to the anterior portion of the blade. There are transitions 
between this partial development of the denticle and full development of the denticle 
itself. 
Gnathodus nodosus Bischoff 
Plate 19, figs. 16a—20c 
1957 Gathodus commutatus nodosus Bischoff (partim) : 23-24, Pl. 4, figs. 12, 13. 
1957 Gnathodus commutatus nodosus Bischoff ; Ziegler in Fliigel & Ziegler : 40, Pl. 111, fig. 4. 
