74 BRITISH AVONIAN CONODONT FAUNAS 
anterior bar. This is well shown by the view of the specimen illustrated on PI. 1, 
fig. 4 of Clarke. It seems, therefore, that the specimens described by Rexroad and 
Collinson must be excluded from the species, for in them the anterior bar does not 
appear strongly laterally expanded. Material from both Scotland and the North 
Crop representing this species is fragmentary but the anterior bar shows the charac- 
teristic very strong lateral expansion. 
Apatognathus scalenus Varker 
Plate 20, figs. ga—11b 
1963 Apatognathus ? gemina (Hinde) Rexroad & Collinson : 8-9, Pl. 1, figs. 12-17. 
1967 Apatognathus ? scalena Varker : 136, 137, Pl. 18, figs. 1, 2, 4, 5. 
MATERIAL. 10 specimens : figured, X 47, X 48, X 49. 
RANGE. North Crop CYD 6-3D 14/15. 
DeEscRIPTION. The characteristic features of this species are the strong lateral 
flexing of the anterior bar, the general form of the unit, the development of a strong, 
elongate, laterally compressed denticle at the apex, an apical angle of about 30° in 
lateral view, and the development of at least one strong denticle in the medial portion 
of the posterior bar. 
Varker has given a detailed description of this species. The anterior bar is about 
equal in length to or slightly longer than the posterior. It bears 10-14 laterally 
compressed, pointed, sharp edged, basally confluent, inwardly curving denticles, 
which increase in size proximally. The apical denticle is at least two to three times 
as long as the largest of the remaining denticles ; it has sharp anterior and posterior 
margins and a convex inner lateral face, the convexity decreasing distally. The 
posterior bar develops about 10 denticles, of which the one in the medial position is 
twice as large as its neighbours and slightly larger than that adjacent to the apical 
denticle. These denticles are rather less closely spaced than those of the anterior 
bar, and in some of them even the basal surfaces are discrete ; they are sharply 
pointed and stand more or less erect to the bar, but those nearest the apical denticle 
are recurved so that they lie more or less parallel to it. The lateral faces of both bars 
are marked on the inner side by a more or less conspicuous shoulder below the origin 
of the denticles. 
Both bars are twisted laterally and they diverge when viewed orally at an angle of 
about 30°, as well as being twisted in a horizontal plane, so that in oral view all the 
denticles radiate away from the apical area. 
In outer lateral view a conspicuous longitudinal ridge is developed at about mid- 
height. In both bars the aboral surface is excavated by a narrow slit-like groove, 
which is only slightly expanded below the apical denticle. 
REMARKS. In some specimens the posterior bar is marked by the development 
of two conspicuously large denticles, although one of these is always larger than the 
other. 
