240 BRITISH AVONIAN CONODONT FAUNAS 
height rapidly near the posterior termination. The aboral outline of the unit is 
arched, the basal cavity being elongate and without flared lips. 
REMARKS. This species appears to be dissimilar to all other described species of 
spathognathodids, although it is closest to S. crassidentatus. 
Spathognathodus sp. B 
Plate 7, figs. 8a—c 
MATERIAL. 4 specimens : figured, X 406. 
RANGE. North Crop ZLA 5, Avon Gorge Z 34-C 7. 
DEscRIPTION. The bar is fairly massive being highest anteriorly, with the height 
decreasing regularly to the posterior ; the posterior termination is broken. The 
anterior-aboral portion of the blade is extended anteriorly as a short flattened 
process. The denticles, at least 17 in number, are laterally compressed and fused 
over the majority of their length. One lateral denticle occurs immediately anterior 
to the anterior margin of the cavity, and reaches the height of the main blade 
denticles. The aboral profile of the unit is not straight, the cavity tending to arch 
the posterior part upward. 
In aboral view the cavity is elongate and moderately flared, extending as a groove 
for a short distance posteriorly and anteriorly. 
REMARKS. This form is probably a pathological variant of S. cf. robustus, the 
lateral dentition placing it in an intermediate position between this and Pseudopoly- 
gnathus sp. 
Spathognathodus sp. nov. 
Plate 6, fig. 9 
MATERIAL. 15 specimens : figured, X 518. 
LOCALITY AND HORIZON. Avon Gorge. Sample Z 1g. 
RANGE. Avon Gorge Z 13-Z 19. 
DeEscriIPTION. A spathognathodid characterized by finely developed oral denticu- 
lation on a bar which is deep and protruding antero-aborally, becoming shallower 
towards its posterior end. The bar is strongly recurved in its posterior half. The 
basal cavity is strongly expanded laterally, and one or more lateral denticles are 
developed on the oral edge. The whole unit tends to be gently curved in a horizontal 
plane, and is clearly transitional towards a pseudopolygnathid condition. 
The basal bar is deepest anteriorly, and the anterior edge and antero-aboral 
margin make an angle of about 70° with one another, so that the antero-aboral 
angle protrudes strongly when seen in lateral view. The basal bar decreases in 
depth posteriorly. The anterior third has a straight aboral margin, but the posterior 
two thirds tend to be gently but continuously arched. The posterior end is bluntly 
spatulate. The oral surface bears a series of closely spaced acicular denticles, 
of which only the apices tend to be discrete. They are long, slender, and subequal 
