BRITISH AVONIAN CONODONT FAUNAS 117 
DESCRIPTION. The anterior arch is broken but appears to be formed by aboro- 
lateral extensions of the basal cavity. The apical denticle is recurved posteriorly ; 
it has a convex anterior margin, lateral keels, and a concave posterior depression, 
becoming obsolescent toward the anterior arch. The posterior bar is formed by an 
extension of the posterior lip of the basal cavity and bears at least one inclined 
denticle. 
The basal cavity is large, the aboral region of the apical denticle being completely 
excavated. 
Subgenus HIBBARDELLA (HASSOGNATHUS) nov. 
TyPE SPECIES. Tvrichognathus separata Branson & Mehl 1934. 
Hibbardella (Hassognathus) separata (Branson & Mehl) 
Plate 25, figs. 13a-14 
1934 Tvichognathus sepavata Branson & Mehl : 290, Pl. 23, fig. 30. 
1934 Tvichognathus breviolata ? Branson & Mehl: 291, Pl. 23, fig. 29. 
1938 Tvichognathus sepavata Branson & Mehl ; Branson & Mehl: PI. 33, fig. 42. 
1939 Tvichognathus sepavata ? Branson & Mehl ; Cooper: 421, Pl. 46, figs. 45, 49. 
1944 Trichognathus sepavata Branson & Mehl; Branson & Mehl, im Shimer & Shrock: 243, 
Pl. 93, fig. 72. 
1944 Tvrichognathus sepavata Branson & Mehl; E. B. Branson: Pl. 32, fig. 42. 
1959 Roundya sp. B Hass: 385, Pl. 46, fig. 11. 
MATERIAL. 58 specimens : figured, X 150, X 149. 
RANGE. North Crop KL 19-ZLA 27, Avon Gorge K 21-C 17. 
DescripTion. The posteriorly recurved apical denticle is tall and ovate in cross- 
section, being thickest at the anterior. The anterior arch is short with the anterior 
bars diverging at about 120°. The bars are narrow, each bearing 3 to 4 short, sub- 
circular posteriorly inclined denticles. The posterior bar is relatively long, being 
thick at the anterior end, and becoming much thinner over the posterior half, where 
it bears a few fine posteriorly inclined denticles. 
In aboral view the unit is excavated, with a large cavity occurring beneath the 
apical denticle and extending along the posterior bar, but becoming gradually 
narrower and ending abruptly. A faint groove runs for a short distance from the 
cavity along either limb of the anterior arch. 
RemMARKS. The large basal cavity distinguishes this species from H. macro- 
dentata. 
Hibbardella (Hassognathus) ? sp. 
Plate 31, fig. 3 
MATERIAL. I specimen : figured, X 319. 
RANGE. Scotland DUN 77. 
