98 BRITISH AVONIAN CONODONT FAUNAS 
the development of a second row. There is a uniform sharp slope towards the 
margin. The platform is arrow-shaped, being widest at the anterior. It becomes 
pointed towards the posterior. The inner platform extends further anteriorly than 
does the outer. The denticulate blade is equal in length to the platform. In lateral 
view, the oral and aboral edges of the blade are straight ; the oral and aboral edges 
of the platform are slightly curved. The anterior and posterior edges are straight. 
REMARKS. Specimens from the Zg beds of the Avon Gorge have a row of nodes on 
either side of the carina. In some examples, the anterior nodes of the inner side of 
the platform are fused to form a parapet. These forms are considered to be transi- 
tional with Gnathodus sennglaber, or possibly with Gnathodus antetexanus. 
This species is common in conodont faunas of late Kinderhookian and early 
Valmeyerian age in North America. Rexroad & Scott (1964) after studying 
hundreds of specimens, came to the conclusion that the low, broad, asymmetrical 
outline of the platform, and the linear arrangement of nodes seem to be consistent 
characters, and similar specimens obtained in the present study have, therefore, been 
placed in this species. 
Gnathodus girtyi girtyi Hass 
Plate 17, figs. ga—-12d 
1953 Gnathodus girtyi Hass : 80, Pl. 14, figs. 22-24. 
1956 Gnathodus girtyi Hass ; Elias : 118, Pl. 3, figs. 30, 31. 
1957 Gnathodus girtyi Hass ; Bischoff (partim) : 24-25, Pl. 4, figs. 16-17, 22-23 (non Pl. 4, 
fig. 21=Gnathodus girtyi simplex Dunn). 
1957 Gnathodus girtyi Hass: Lys & Serre : 1043, Pl. 2, figs. 7a—c. 
1958 Gnathodus ? sp. Rexroad : 18, Pl. 1, figs. 3-5. 
1960 Gnathodus clavatus Clarke : 28, Pl. 4, figs. 4-6 (non Pl. 4, figs. 7-9=G. girtyi simplex 
Dunn). 
1961 Gnathodus givtyi Hass ; Higgins : 220, Pl. fo, fig. 4. 
1961 Gnathodus n. sp. Rexroad & Collinson : PI. 1. 
1961 Gnathodus givtyi Hass ; Rexroad & Jarrell : 2015. 
1962 Gnathodus girtyi Hass ; Collinson, Scott & Rexroad : Chart 4. 
1962 Gnathodus givtyi Hass Form A Meischner : 31, text-fig. Io. 
1963 Gnathodus girvtyi Hass Form C Bouckaert & Higgins : 17, text-fig. 3. 
Gnathodus girtyi givtyi Hass ; Collinson & Druce in press. 
MATERIAL. 780 specimens : figured, X 103, X 104, X 105, X 106. 
RANGE. North Crop CYD 5-3D 23, Avon Gorge D 26. 
DESCRIPTION. The main features of this subspecies have been described in detail 
by Collinson & Druce (in press) and the present specimens, although showing 
some variation, agree in all major respects with their description. The most 
distinctive features are the long slender form of the unit, with the anterior blade 
commonly being strongly laterally compressed and relatively high in relation to its 
length ; it occupies at least half the total length of the unit. It is straight to curved 
in oral view. The unit as a whole is straight or curved in a horizontal plane, and the 
curvature is chiefly concentrated in the posterior portion of the carina (e.g. Pl. 17, 
