102 BRITISH AVONIAN CONODONT FAUNAS 
On the outer-lateral margin of the platform one or two low rounded denticles are 
developed. These tend to be developed about midway along the length of the 
platform, and are visible but not conspicuous in lateral view. 
The aboral cavity is large and flared, and the quadrate outline of the outer lateral 
margin of some specimens is strongly reminiscent of G. bilineatus. 
Gnathodus girtyi turritus Collinson & Druce 
Plate 31, fig. 23 
1957 Gnathodus girtyi Hass ; Bischoff: 24, 25, Pl. 4, figs. 18-20 (non figs. 16, 17, 22, 23= 
Gnathodus girtyi givtyi Hass ; non pl. 4, fig. 21=G. girtyi simplex Dunn). 
Gnathodus girtyi turritus Collinson & Druce in press. 
MATERIAL. 5 specimens : figured, X 116. 
RANGE. North Crop 3D 19-3D 23. 
DEscRIPTION A subspecies of G. girtyi with a low posteriorly reduced carina. 
The lateral denticle ridges are generally continuous around the posterior edge of 
the platform. The sides of the posterior platform are nearly vertical. 
REMARKS. The subspecies is extremely rare in our collections. Transitional 
specimens of G. girtyi girtyi are present in faunas from Yorkshire and the North Crop. 
It is difficult to refer these transitional specimens to one or other subspecies with any 
certainty. 
Gnathodus girtyi subsp. nov. A 
Plate 17, figs. 1a—3d 
MATERIAL. 3 specimens : figured, X 117, X 118, X 119. 
Rance. North Crop CYD 7. 
DEscRIPTION. A subspecies of G. girtyi characterized by the development of 1 or 
2 vertical lateral pillars near the anterior inner end of the platform. The pillars 
extend from the oral surface almost to the aboral margin. 
The three specimens upon which this new subspecies is based show the general 
features which are characteristic of G. girtyi girtyi. They differ from that subspecies, 
however, in being left forms in which the longer inner lateral denticulated margin of 
the platform is produced downwards by an unornamented, vertical column. In one 
specimen (PI. 17, figs. 3a—d) this column reaches the aboral margin which is deflected 
by it. In this particular specimen the vertical pillar occurs about one quarter of the 
platform length behind the anterior end of the inner lateral denticle ridge. In the 
specimen illustrated in Pl. 17, fig. 1, the vertical pillar occupies the same relative 
position but is much less conspicuous, and the lateral margin only is conspicuously 
offset by it. In this specimen the oral margin of the denticulation is not disturbed in 
any way by a development of the lateral pillar. In the specimen shown in PI. 17, 
fig. 2, two sharply angular vertical ridges are developed in the same relative position, 
but neither of these extends into the aboral margin ; between them there is a 
