BRITISH AVONIAN CONODONT FAUNAS 197 
RANGE. North Crop ZLA 3-ZLA 27. 
Description. The anterior bar is short, bearing about 5 discrete, sub-circular, 
posteriorly inclined denticles, whose height increases posteriorly, culminating in the 
apical denticle, which is the largest. The posterior bar is very restricted, commonly 
bearing I or 2 small, discrete, sub-circular, posteriorly inclined denticles. 
In aboral view the whole unit is excavated, the basal cavity being expanded and 
pear-shaped at the posterior end. The widest part occurs beneath the apical denticle 
and it narrows gradually beneath the anterior bar, and rapidly beneath the posterior 
bar. The posterior termination tends to be rather blunt. The cavity lips in the 
posterior part are thickened to give a small flange. 
RemMArKS. The large basal cavity with excavated bars, together with the short 
posterior bar, precludes the placing of this species within the genus Ozarkodina, and 
serve to distinguish it from all other prioniodinids. 
Prioniodina prelaevipostica sp. nov. 
Plate 24, figs. 1-6 
DERIVATION OF NAME. Ancestral form of Prioniodina laevipostica (Rexroad & 
Collinson). 
Diacnosis. Short Prioniodina, with large apical denticle and deflected anterior 
bar. 
MATERIAL. 9g specimens: Holotype X 334, Paratypes X 333, X 331, X 332, 
X 335, X 336 (all figured). 
TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, uppermost Z Zone. 
Sample ZLA 33. 
Rance. North Crop ZLA 32-ZL 109. 
Description. The whole unit is arched, being surmounted by a tall, laterally 
compressed, free standing, posteriorly inclined apical denticle. The anterior bar is 
short, depressed through 45° and slightly deflected, bearing 2 or 3 tall isolated 
denticles, the most anterior ones being very small and posteriorly inclined. 
The posterior bar is longer than the anterior, being fairly deep, shallowing 
posteriorly, and bearing 4 or 5 triangular denticles which are laterally compressed 
and posteriorly inclined. 
In aboral view the unit is excavated beneath the apical denticle and the posterior 
bar, the cavity having flared lips. Beneath the anterior bar there is a narrowing 
groove. 
Remarks. This species is very similar to P. laevipostica (Rexroad & Collinson) 
which should be referred to the genus Prioniodina. The two species differ in the 
degree of curvature of the anterior bar, our species being much less curved, and in the 
dentition of the posterior bar, on which P. laevipostica bears 4 or 5 well-formed 
denticles. The obvious morphological similarities of these two species lead us to 
believe that P. prelaevipostica is the precursor of P. laevipostica. 
