196 BRITISH AVONIAN CONODONT FAUNAS 
individuals bear up to five closely set, but apically discrete, more or less sharply 
pointed denticles, which decrease in size posteriorly and which are inclined at about 
45° to the aboral surface of the posterior bar. The posterior bar is deep in its 
anterior portion but tapers rapidly towards its posterior end. Its aboral margin is 
more or less straight. 
The apical denticle is two to three times the width of the largest adjacent denticles 
and is sharply to bluntly pointed. There is considerable variation in the form of the 
distal end of the apical denticle (see Rexroad & Collinson 1963). Although the 
cavity is similar in general form, it is rather shallower andsomewhatlessasymmetrical 
than that of P. eiveica, and its anterior extension is also rather more conspicuous. 
The edges of both the cavity and the slits along the anterior and posterior bars are 
also prominent. 
REMARKS. Our specimens from the D Zone closely resemble those of Rexroad & 
Collinson in overall morphology and in the aboral configuration, but they differ in 
denticulation, our specimens having fewer denticles on the anterior bar and more on 
the posterior bar. However, Rexroad & Collinson mention that some of their 
specimens fall within the limits of our specimens. The variable dentition is thus 
due to variation within the species. 
Prioniodina latericrescens (Branson & Mehl) 
Plate 24, fig. 19 
1934 Lonchodina latericrescens Branson & Mehl : 212, Pl. 14, fig. 20. 
MATERIAL. 12 specimens : figured, X 429. 
Rance. North Crop KL 1-ZLA 4. 
DESCRIPTION. The unit is bowed and arched, being laterally compressed in 
juveniles, but the bars becoming circular in cross-section in adults. The posterior 
and anterior bars are of equal length, bearing about 4 isolated, sub-circular, 
posteriorly inclined denticles. In aboral view the pit is fairly large and occurs 
beneath the apical denticle. 
Prioniodina oweni sp. nov. 
Plate 28, figs. 5a—c 
DERIVATION OF NAME. After Mr. T. R. Owen. 
DraGnosis. Prioniodinid with greatly expanded basal cavity and restricted 
posterior bar. 
MATERIAL. 13 specimens : Holotype X 330 (figured). 
TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, Lower Z Zone. Sample 
ZLA 5. 
