112 BRITISH AVONIAN CONODONT FAUNAS 
MATERIAL. 3 specimens : figured, X 508. 
RANGE. North Crop CYD 7-3D 8. 
DeEscrRIPTION. Rexroad & Collinson (1963) have shown that the holotype of this 
species is broken and that the limbs are longer than the original description suggests. 
The present specimens are fragmentary, but they show the specific characteristics. 
The posterior bar tends to be rather strongly developed, and the lateral bars are 
sharply flexed posteriorly. 
Hibbardella (Hibbardella) acuta Murray & Chronic 
Plate 25, figs. Iga—20 
1961 Hibbardella fragilis Higgins : 213, Pl. 12, fig. 4, text-fig. 2. 
1963 Hibbardella fragilis Higgins ; Bouckaert & Higgins : 17, fig. 3. 
1965 Hibbardella acuta Murray & Chronic : 598, Pl. 73, figs. 3-5. 
Hibbardella higginsi Collinson & Druce in press. 
MATERIAL. Ig specimens : figured, X 139, X 422. 
RANGE. North Crop 3D 4-3D 17. 
DescriPTION. The most distinctive features of this species are the greatly 
elongated anterior and posterior bars, the relatively slender denticulation and the 
lateral twisting of the anterior bars. The apical denticle, although relatively long, is 
only about half the length of the anterior bars ; it is slender, with a feebly convex to 
flat anterior face and sharp lateral edges ; the posterior part of the face of the apical 
denticle is developed into a posterior knife edge, the posterior lateral faces tending to 
be rather flat. The anterior bars are long and are longitudinally twisted so that the 
denticles tend to originate from the anterior surface. The bars bear up to Io lateral 
denticles which are basally confluent but apically distinct and are more or less com- 
pressed anterior-posteriorly. In addition to their longitudinal flexure, the bars are 
recurved posteriorly, so that their anterior faces are gently convex. They diverge 
from each other at an angle of about 30°. 
The posterior bar is elongated and decreases in depth posteriorly. Its aboral 
margin is gently concave, most of the curvature being concentrated near the mid- 
point of the unit. Its oral surface bears a series of confluent, but apically distinct, 
hindeodellid-type denticles. The larger members of the series tend to increase in 
size toward the mid-point of the bar, and then to decrease toward the posterior end. 
There are about 8 or g main denticles, each separated by two or three smaller 
denticles. The denticles are more or less laterally compressed, but tend to have 
rather strong convex lateral faces. The lateral faces of the posterior bar are gently 
convex. The whole appearance of the posterior bar is strikingly deep and elongated. 
Shallow longitudinal slit-like grooves extend along the anterior and posterior bars, 
and there is a very small pit below the apical denticle. 
