BRITISH AVONIAN CONODONT FAUNAS 175 
denticle, are fused for the greater part of their length, and are highest near the apical 
denticle. They decrease in height uniformly to the anterior and posterior extremi- 
ties. The basal cavity is small and thin, and is situated beneath the apical denticle. 
Ozarkodina plana (Huddle) 
Plate 27, figs. I-3 
1934 Bryantodus planus Huddle : 75-76, Pl. ro, fig. 8. 
non 1934 Bryantodus planus Huddle ; Branson & Mehl: 284, Pl. 23, fig. 8. 
1957 Ozarkodina cf. O. plana (Huddle) Rhodes & Dineley : 364, Pl. 37, fig. 24. 
1961 Ozarkodina plana (Huddle) Scott & Collinson : 128, Pl. 2, fig. 8. 
MATERIAL. 12 specimens : figured, X 300, X 301, X 419. 
Rance. Avon Gorge K 3-Z 15. 
DESCRIPTION. The anterior and posterior blades are short, slightly arched, 
laterally compressed, and very thin. The apical denticle is short, broad at the base, 
acutely pointed and situated slightly anterior to the basal cavity. The blade 
denticles are similar in outline to the apical denticle and usually number 4 anteriorly 
and 6 posteriorly. The basal cavity is small and situated slightly anterior to the 
apical denticle. 
Ozarkodina plumula Collinson & Druce 
Plate 27, figs. 4, 5 
Ozarkodina plumula Collinson & Druce (in press). 
MATERIAL. 4 specimens : figured, X 302, X 303. 
RANGE. North Crop 3D 12. 
DescripTion. The diagnostic characteristic of this species is the slender elon- 
gated anterior bar, bearing a large number of small, posteriorly inclined denticles. 
The posterior bar is shorter and deeper, and bears a smaller number of conspicuously 
larger denticles than those of the anterior bar. The apical denticle is only slightly 
larger than the largest of the posterior bar and the whole unit is more or less con- 
tinuously recurved. The anterior bar is of slender elongate construction, relatively 
shallow in depth, and bears a series of up to 12 small confluent denticles, only the 
apical tips of which are discrete. These are sharply inclined to the anterior bar and 
tend to decrease in size posteriorly. 
The apical denticle is only slightly larger than those adjacent to it both in length 
and in width. It is, however, conspicuously more sharply inclined than most of 
those of the anterior bar, and in this it parallels the denticles of the shorter posterior 
bar. It is very strongly laterally compressed, with sharp anterior and posterior 
edges, and is confluent with the posterior denticles for the greater part of its posterior 
margin, though its inclination removes most of its anterior edge on the adjacent 
anterior denticles. 
The denticles of the posterior bar are similar to, but rather larger than, those of the 
