04 BRITISH AVONIAN CONODONT FAUNAS 
features of the species. They are very similar to the specimens illustrated by 
Rexroad and Scott. 
Gnathodus avonensis sp. nov. 
Plate 18, figs. ga—d 
DERIVATION OF NAME. After the type section in the Avon Gorge. 
DiaGnosis. Gnathodus avonensis sp. nov. is closely similar to Gnathodus simplicatus 
sp. nov. but bears a node on one side of upper surface of platform. 
MATERIAL. 2 Specimens : Holotype X 411 (figured). 
TYPE LOCALITY AND HORIZON. Avon Gorge Zz Limestone. Sample Z 38. 
RANGE. Avon Gorge Z 38. 
Description. The platform is confined to the posterior third of the unit and is 
unornamented except for the presence of a single node on one side of the platform. 
It is biconvex in outline and narrow. In lateral view the blade is rather rectangular 
in outline, the 10 or more denticles being of uniform size. The anterior edge is 
straight, and forms a right angle with the aboral edge of the blade, which may be 
slightly curved. The oral edge is straight in the anterior half of the unit and slightly 
arched in the posterior half of the unit. The platform has a concave aboral margin 
in lateral view, and is less deep than the blade. There is a flaring and elongate 
basal cavity below the platform. 
REMARKS. Gnathodus avonensis sp. nov. developed from G. simplicatus sp. nov. 
by the formation of a single node on the side of the platform. G. avonensis sp. nov. 
is a homoeomorph of G. nodosus Bischoff. 
Gnathodus bilineatus (Roundy) 
Plate 18, figs. 14a-17d 
1900 Polygnathus (Gnathodus) Mosquensis Pander (sic) Hinde : 342, Pl. 9, figs. 2-4. 
1926 Polygnathus bilineatus Roundy : 13, Pl. 3, figs. toa—c. 
1926 Polygnathus texanus Roundy : 14, Pl. 3, figs. 13a, b. 
1928 Gnathodus mosquensis (Pander) Holmes : 6, fig. 31. 
1939 non Gnathodus bilineatus Cooper : 388, Pl. 42, figs. 59-60. 
1941 Gnathodus pustulosus Branson & Mehl: 172, Pl. 5, figs. 32-39. 
1953 Gnathodus bilineatus (Roundy) Hass: 78, Pl. 14, figs. 25-29. 
1956 Gnathodus bilineatus (Roundy) Elias: 118, Pl. 3, figs. 23-29. 
1956 Gnathodus pustulosus (Branson & Mehl) Elias: 115, Pl. 3, figs. 1-8. 
1957 Gnathodus bilineatus bilineatus (Roundy) Bischoff: 21, Pl. 3, figs. 11, 15-20 ; 
Pl. 4, fig. 1. 
1957 Gnathodus bilineatus bilineatus (Roundy) Ziegler im Fliigel & Ziegler : 38, Pl. 3, figs. 
I, 2 only. 
1957 Gnathodus modocensis Rexroad : 30, 31, Pl. 1, figs. 15-17. 
1958 Gnathodus modocensis Rexroad ; Rexroad: 17, 18, Pl. 1, figs. 1, 2. 
1959 Gnathodus bilineatus (Roundy) Voges: 282, Pl. 33, figs. 28-30. 
1959 Gnathodus (Harltonodus) bilineatus (Roundy) Elias : 145, Pl. 1, figs. 3-12. 
1959 Gnathodus (Harltonodus) bransom Elias : 147, Pl. 1, figs. 13-18. 
1959 Gnathodus (Harltonodus) minutus Elias : 148, Pl. 1, figs. 22-25. 
1959 Gnathodus (Harltonodus) multilineatus Elias : 149, Pl. 1, figs. 26-28. 
