BRITISH AVONIAN CONODONT FAUNAS 115 
the distinctive form of the apical denticle, and in the characteristic angle of the 
anterior bars as seen in the vertical plane. In H. (H.) ortha this angle approaches 
go° but it is nearer 180° in H. (H.) parva. H. (H.) ortha also lacks the strong 
posterior recurvature of the apical denticle and the denticles of the anterior bar. 
Hibbardella (Hibbardella) cf. macrodentata Thomas 
Plate 25, figs. 16a-18c 
1949 Hibbardella macrodentata Thomas : 422, Pl. 4, fig. 25. 
MATERIAL. 75 specimens : figured, X 147, X 148, X 146. 
RANGE. North Crop KL 2-ZLA 33, Avon Gorge K3-Z 38. 
DESCRIPTION. The apical denticle is tall, laterally compressed and inclined 
posteriorly. The anterior arch is deep with each limb curved posteriorly. The 
anterior bars diverge at an angle of approximately go°, and the aboral edge of the 
anterior bars is lower than that of the posterior bar. The denticles of the arch are 
isolated, sub-circular and of unequal height. The posterior bar is narrow, long 
(though broken in the majority of our specimens) and finely denticulate. All the 
denticles are sub-circular and posteriorly inclined. The cavity is minute and 
situated beneath the apical denticle. 
REMARKS. The holotype is broken, but, from Thomas’s illustration and description 
it would appear that our specimens are very close to H. macrodentata. Although 
Thomas describes the posterior bar as blunt and non denticulate, the holotype 
(shown in PI. 4, fig. 25) is clearly broken. 
Hibbardella (Hibbardella) sp. 
Plate 25, figs. 15a, b 
MATERIAL. I specimen: figured, X 441. 
Rance. North Crop KL 16. 
DESCRIPTION. This specimen is characterized by the massive form of its anterior 
bars. The anterior bars are short, deep and strongly downcurved, their oral and 
aboral margins being strongly convex in anterior view, although there is a conspic- 
uous indentation in the aboral profile below the apical denticle. The strongest 
downflexing is in the distal thirds of the bars. The lateral faces of the anterior bars 
are convex, and both are characterized by prominent longitudinal ridges developed 
just below mid-height, and extending along the length of the bars. The oral surfaces 
of the anterior bars bear up to six discrete and rather stout denticles, the largest being 
in the medial portions of the bars. They are discrete, more or less rounded in cross- 
section, and the larger ones are slightly inflexed towards the apical denticle. Their 
length is unknown, but the largest is longer than the depth of the basal bars. The 
ends of the bar are spatulate. 
The apical denticle is relatively slender, being only slightly greater in width than 
the largest of the denticles of the anterior bars. The anterior face is rounded, but 
