134 BRITISH AVONIAN CONODONT FAUNAS 
Ligonodina levis Branson & Mehl 
Plate 26, figs. 15a, b, 17a-19b 
1941 Ligonodina levis Branson & Mehl: 185, Pl. 6, fig. 10. 
1949 Ligonodina sp. Youngquist & Miller (partim) : 620, Pl. ror, figs. 12 & 13 only. 
1957 Ligonodina levis Branson & Mehl ; Bischoff: 30, Pl. 5, figs. 8, 9, Pl. 6, fig. 25. 
1957 Ligonodina obunca Rexroad : 32, Pl. 1, figs. 22, 23. 
1958 Ligonodina obunca Rexroad ; Rexroad : 21, Pl. 3, figs. 7, 8. 
1961 Ligonodina levis Branson & Mehl ; Rexroad & Burton: 1154, Pl. 141, figs. 7, 8. 
1963 Ligonodina levis Branson & Mehl ; Thompson & Goebel : 11, fig. 3. 
1963 Ligonodina levis Branson & Mehl ; Rexroad & Collinson : 11, Pl. 2, figs. 24, 25. 
1964 Ligonodina levis Branson & Mehl; Rexroad & Furnish : 672, Pl. 111, fig. 381. 
1965 Ligonodina levis Branson & Mehl; Rexroad & Nicoll: 21, Pl. 2, fig. 24. 
MATERIAL. 25 specimens : figured, X 204, X 205, X 206, X 207. 
RANGE. North Crop CYD 6-3D 14/15, Avon Gorge Z 38-D 26. 
DESCRIPTION. Rexroad’s original description of this particular species was rather 
generalized, but the distinctive features seem to be the massive and rather rounded 
main denticle, which is continuously recurved, especially in its lower part, so that its 
distal portion makes an angle of about 45° with the posterior bar. The distal 
portion is not greatly laterally compressed, although it has sharp anterior and 
posterior edges ; the lateral faces are themselves strongly convex. The posterior 
edges become obsolescent towards the proximal end. The outer lateral aboral 
surface is expanded slightly laterally, but has a conspicuous flange-like structure 
developed along it, which slopes towards the aboral cavity. The proximal inner 
portion of the main denticle is very strongly convex. 
The posterior bar is of unknown length but is more or less quadrate in cross-section, 
with a broad aboral edge. It bears at least one, stump-like denticle, which is well 
separated from the base of the main denticle. The antero-aboral surface of the main 
denticle tends to be rather rounded, and in oral-outer lateral view extends below the 
main level of the denticle in a rather bluntly pointed termination. The main 
denticle extends in a continuous curve downward to form the inner anterior aboral 
process. The aboral surface of this process lies at an acute angle, often as small as 
45°, to the posterior bar. Its oral surface bears up to 5 large denticles, of which 
those at the anterior end tend to be very large. They are straight to slightly curved 
Main denticle Bees 
Inner-lateral 
lamina 
if ff 
E (i 4 Posterior denticles 
Posterior bor 
Anterior aboral 
process 
Fic. 27. Ligonodina sp. showing morphological terms used in the text. 
