182 BRITISH AVONIAN CONODONT FAUNAS 
variable size, inclined posteriorly ; at or near posterior end of unit a relatively 
enormous, greatly elongated denticle, slightly greater in basal width than apical 
denticle. 
The inner lateral face is generally convex, with a rather flat oral shoulder on which 
the denticles are developed. The denticulation of the anterior bar consists of a 
series of rather small inconspicuous basally confluent denticles, all inclined equally 
posteriorly at an angle of about 45° to the oral edge of the bar. The anterior end is 
roundly spatulate and there is a very feeble basal flare below the apical denticle. 
The apical denticle is biconvex in cross-section, with blunt anterior and posterior 
edges, and is curved slightly inward, as well as being inclined posteriorly. On the 
posterior bar there is a series of denticles which decrease in size towards the distal 
end ; they are basally confluent and have sharp free tips, the most posterior, or the 
one next to it, being much the largest. The posterior portion of the posterior bar is 
straight-edged, but the posterior aboral corner is bluntly rounded. The whole aboral 
surface of the unit is gently concave in lateral view and the unit tends to be bowed 
inwards, as well as the main denticles being rather incurved. In outer lateral view 
the whole unit is rather flat and is slightly indented below the apical denticle. The 
basal surface is flared on the inner lateral face below the apical denticle, and there is a 
broad cavity in this position, which rapidly decreases anteriorly and posteriorly, to 
be extended along part of both bars as a shallow longitudinal slit. 
Genus POLYGNATAUS Hinde 1879 
1879 Polygnathus Hinde : 359. 
TYPE SPECIES. Polygnathus dubia Hinde 1879. 
Polygnathus communis communis Branson & Mehl 
Plate 12, figs. 2a—5c 
1934 Polygnathus communis Branson & Mehl: 293, Pl. 24, figs. 1-4. 
1934 Polygnathus communis Branson & Mehl ; E. R. Branson : 308, Pl. 25, figs. 5, 6. 
1938 Polygnathus communis Branson & Mehl; Branson & Mehl: 145, Pl. 34, figs. 39-41. 
1939 Polygnathus communis Branson & Mehl ; Cooper : 399, Pl. 39, figs. 1, 2, 9, 10, 23, 24. 
1939 Polygnathus adola Cooper : 399, Pl. 39, figs. 33-36. 
1939 Polygnathus marginata Branson & Mehl ; Cooper: 4o1, Pl. 41, figs. 15, 16. 
1944 Polygnathus communis Branson & Mehl ; Branson & Mehl im Shimer & Schrock : 245, 
Pl. 94, figs. 29-31. 
1944 Polygnathus communis Branson & Mehl; E. B. Branson : 208, 221, Pl. 39, figs. 39-41. 
1947 Polygnathus communis Branson & Mehl ; Mehl & Thomas: 15, PI. 1, fig. 36. 
1949 Polygnathus communis Branson & Mehl; Youngquist & Patterson: 62, Pl. 15, figs. 
7; 8: 
1949 Polygnathus communis Branson & Mehl ; Thomas: 411, Pl. 3, fig. 70. 
1951 Polygnathus communis Branson & Mehl ; Youngquist & Downs: 787, Pl. 111, figs. 
4, 5, 19, 20. 
1951 Polygnathus communis Branson & Mehl ; Hass: 2538, 2539, Pl. 1, fig. Io. 
1956 Polygnathus communis Branson & Mehl ; Bichoff & Ziegler : 156, Pl. 12, figs. 1-3. 
1956 Polygnathus communis Branson & Mehl ; Hass : 24, 25, Pl. 2, figs. 3-5. 
