228 BRITISH AVONIAN CONODONT FAUNAS 
MATERIAL. 278 specimens : figured, X 464, X 465, X 466, X 467, X 468. 
RanGE. North Crop CYD 7, Avon Gorge Z 1—D 26. 
Description. This spathognathodid bears 8 to 12 denticles along its oral edge, 
of which the most anterior is the largest. The remaining denticles decrease uni- 
formly in size towards the posterior end, so that the general form of the denticulate 
edge is continuously convex, being lowest posteriorly. The basal cavity extends for 
about two-thirds the length of the unit. It is widest at the anterior end, and is 
continuous to the posterior end, being biconvex in outline. 
The short blade is distinguished by a deep anterior end, with a high anterior 
denticle. The anterior edge of the unit slopes conspicuously forward so that its 
antero-aboral projection lies in front at the tip of the denticle. The antero-aboral 
angle is either bluntly rounded or more or less angular, forming an angle of about go°. 
The anterior edge is straight. The anterior denticle is about half as long again as 
that adjacent to it, and about twice as wide. The remaining denticles of the bar 
decrease uniformly in size towards the posterior end. Except for the two posterior 
denticles which tend to be conspicuously smaller than the rest, the denticles are 
discrete only at their bluntly rounded tips. They have convex lateral faces and 
stand erect to the bar. The posterior margin, which is formed of the two most 
posterior denticles, tends to slope posteriorly. In lateral view the aboral edge of the 
unit is straight in the anterior third of the unit, but is concave posteriorly, because 
of the flare of the basal cavity. This cavity is slightly asymmetrical, but is strongly 
convex in outline and extends for about two thirds the length of the aboral surface. 
Its maximum width is only about half or a third of its total length and its greatest 
depth and width are anterior. It extends anteriorly as a median slit along the 
anterior blade. 
There is a tendency in some specimens for the posterior denticles to be progressively 
posteriorly inclined towards the posterior end. In some specimens the anterior 
aboral angle is rather less than go° and the apical denticle is more sharply triangular 
in lateral view than in other specimens. 
REMARKS. The first stratigraphic occurrence of Spathognathodus cristulus in the 
Avonian of the Bristol area is considerably older than that known in other parts of 
the world. 
Spathognathodus elongatus (Branson & Mehl) 
Plate 7, figs. ra—5b 
1938 Spathodus elongatus Branson & Mehl : 139, Pl. 34, fig. 6 (non Pl. 34, fig. 9 = S. crassi- 
dentatus?). 
1944 Spathodus elongatus Branson & Mehl; E. B. Branson: Pl. 39, fig. 6, (non Pl. 39, fig. 
9 = S. crassidentatus?). 
MATERIAL. 48 specimens: figured, X 472, X 473, X 474, X 475. 
Rance. North Crop KL 19-ZL 8, Avon Gorge K 4-Z 13. 
DEscRIPTION. The blade is straight or gently curved in oral view, being long and 
