BRITISH AVONIAN CONODONT FAUNAS 145 
Magnilaterella complectens (Clarke) 
Plate 23, figs. 14a-17c 
1900 Prioniodus tulensis Hinde (partim) : 343, Pl. 9, fig. 16. 
1928 Prioniodus tulensis Hinde ; Holmes (partim) : 22, Pl. 3, fig. 20. 
1960 Ligonodina complectens Clarke : 9, Pl. 1, figs. 14, 15. 
MATERIAL. 14 specimens : figured, X 240, X 237, X 238, X 239. 
RANGE. Scotland HOSIE 2A—-HOSIE 2B. 
DESCRIPTION. This species is clearly a member of the genus Magnilaterella 
Rexroad & Collinson, but is not typical of that genus. The generic features are seen 
in the present specimens in the short form, strong inner lateral callus and basal 
groove of the lateral bar, and the deflected and upflexed general form of the posterior 
bar, the largest denticles of which are situated at the proximal end and which are 
strongly developed and strongly recurved and incurved. In contrast to other 
described forms of the genus Magnilaterella, however, the largest denticles of the 
lateral bar are situated at the anterior, and not at the posterior end. This form, 
therefore, seems to approach Ligonodina, to which Magnilaterella is closely related. 
Rexroad & Collinson (1963 : 13) have discussed the relationships between the two 
genera, but the character of the present specimen alters the view of the distinctive 
nature of the denticulation of the posterior bar. 
The lateral bar is short and in inner view is deep ; the most anterior denticle is 
enormously developed and strongly recurved in its lower portion, its distal half being 
more or less straight, although the distal posterior edge is so sharply pointed that it 
gives it almost a sigmoidal appearance. The two remaining denticles of the posterior 
bar are inconspicuous by comparison with the major denticle ; they are isolated, 
small, sub-circular, and more or less sharply pointed. The posterior bar is curved 
sharply backward and upward and the proximal denticle is very strongly developed. 
It approaches, but does not quite equal, the major denticle in size ; it is biconvex in 
cross-section, with bluntly developed anterior and posterior ridges in its upper half, 
but in the proximal half it is convex on the anterior face and has a concave posterior 
depression on its posterior edge. The inner lateral face is strongly convex and it 
bears at least one small isolated sub-circular denticle. The largest denticle of the 
posterior bar is recurved and deflected parallel to the major denticle. 
The aboral surface of the unit is conspicuously grooved; the outer aboral surface 
tends to be flat and rather extended below the major denticle, but the inner aboral 
surface is strongly developed as a callus, which runs up the inner face of the lateral 
bar. This slopes down to give a relatively narrow, horizontal, aboral surface, 
parallel to the base of the groove. In more complete specimens the lateral bar is seen 
to taper to a point at its distal end ; it may bear only 2 denticles including the most 
anterior denticle. In more complete specimens the posterior bar may bear up to 6 
denticles in specimens which tend to decrease distally in size ; when viewed orally it 
makes an angle of about 30° with the lateral bar. In the specimen shown in Pl. 23, 
fig. 14 a small and relatively inconspicuous denticle is developed in front of the largest 
