176 BRITISH AVONIAN CONODONT FAUNAS 
anterior. They are about 5 or 6 in number and are strongly laterally compressed 
with sharp anterior and posterior edges and gently biconvex lateral faces. Their 
bases are confluent and their sharply pointed apices discrete. The posterior bar is 
deeper than the anterior, and tends to become shallower towards its posterior end. 
It is inclined to the anterior bar at an angle which varies from 130°-140°, although 
the junction between the two is continuously curved, so that the whole aboral 
margin is concave with more or less straight distal ends. 
There is a relatively inconspicuous flare on the basal margin below the posterior 
edge of the apical denticle. The basal cavity is gently flared, being slightly larger 
than that of many typical ozarkodinids. It is continued as a longitudinal slit along 
both the anterior and the posterior bars, both of which become narrower towards the 
aboral margin. The whole unit is more or less straight in a vertical plane. 
In complete specimens the denticles are seen to be sharply pointed, and the 
denticles of the posterior bar are discrete for a greater part of their length than those 
of the anterior bar. The posterior aboral corner of the posterior bar is very strongly 
rounded and terminates orally in the tip of the posterior denticle. 
Ozarkodina cf. congesta Stauffer 
Plate 27, fig. 13 
1940 Ozarkodina congesta Stauffer : 427, Pl. 59, fig. 12. 
1957 Ozarkodina plana Huddle ; Bischoff & Ziegler 78, 79, Pl. 12, fig. 15a, b. 
1959 Ozarkodina cf. vegularis Branson & Mehl ; Helms: 647, Pl. IV, fig. 15 only. 
MATERIAL. 14 specimens : figured, X 288. 
Rance. Avon Gorge Z 17-Z 37. 
Description. A gently arched unit with symmetrical anterior and posterior 
blades, commonly bearing 7 straight posteriorly inclined denticles, highest near the 
apical denticle, and decreasing in length uniformly to the anterior and posterior 
extremities of the blades. The apical denticle is straight to slightly curved, 
posteriorly inclined and higher and wider than the blade denticles. The small 
circular basal cavity is situated beneath the apical denticle, The aboral edge is 
sharp. 
REMARKS. In the Z beds of the Avon Gorge, specimens of Ozarkodina are found, 
which are neither identical with one another nor with previously described species. 
Reference to the literature shows that previous workers, for example Helms (1959) 
and Bischoff & Ziegler (1957), have often assigned specimens in their studies to 
species where the holotype bears little resemblance to their specimens. In the 
present study, the majority of the Z bed ozarkodinids have been referred to two 
general categories ; O. cf. congesta Stauffer, which has symmetrical anterior and 
posterior limbs, and Ozarkodina macer (Branson & Mehl) which has asymmetrical 
anterior and posterior limbs. 
