BRITISH AVONIAN CONODONT FAUNAS 135 
and are directed inwards and upwards. The denticles are discrete and more or less 
sub-circular in cross-section. 
The antero-aboral process decreases in thickness towards the distal end. The 
aboral surface is characterized by thick, aborally directed, lip-like, flange structures 
along the lateral edges of both the posterior bar and the antero-aboral process. 
There is a pit-like cavity below the main denticle and there are longitudinal grooves 
along the aboral surface of the posterior bar and the antero-aboral process. These 
decrease in width towards the distal end of the process. 
Ligonodina magnilaterina sp. nov. 
Plate 26, figs. 8a—11b 
DERIVATION OF NAME. From the resemblance of the species to the genus Mag- 
nilaterella. 
Diaecnosis. Ligonodinid with a denticle situated anterior to main denticle, 
forming continuation of denticle series of posterior bar. Anterior denticle only 
slightly smaller in size than main denticle, though tending to be rather more slender 
in general form ; lying at junction of antero-aboral process and posterior bar. 
MATERIAL. 6specimens : Holotype X 211, Paratypes (all figured) X 208, X 209, 
270. 
TYPE LOCALITY AND HORIZON. Scotland Sample HOSIE 2C. 
RANGE. Scotland HOSIE 2C. 
DESCRIPTION. The main denticle is strong, the base being strongly developed 
anteriorly and posteriorly. It is of unknown length, sub-circular in cross-section in 
the lower part. The main denticle is recurved in its lower part, the inner and outer 
lateral faces being strongly convex. The posterior margin of the main denticle is 
extended to form the oral surface of the posterior bar. This bar is of unknown 
length, but is deep in its anterior part and bears at least 4 discrete denticles, which 
are only slightly laterally compressed and of variable size. It is possible that they 
may be arranged in a cyclic pattern. 
On the anterior face of the main denticle a thickened denticle is developed at the 
junction of the anterior denticle and the antero-aboral process. This denticle is 
distinct from those of the antero-aboral process and in inner lateral view it seems to 
represent a continuation of the posterior bar. In outer lateral view it may be seen to 
be recurved inwardly at its base ; its anterior face is strongly convex with sharp 
lateral edges. It is recurved slightly posteriorly to lie sub-parallel to the main 
denticle, and also slightly inwardly. It is fused at the base to the main denticle and 
arises from it at a strongly convex junction. It is long and slender, being sharply 
pointed at its distal end and is about half the diameter of the main denticle. The 
other denticles of the anterior aboral process, which number at least three, are 
discrete, sub-circular in cross-section with poorly defined, but rather sharp, lateral 
edges. They tend to decrease in size distally. The anterior aboral process appears 
to be relatively short, although none of the present specimens is complete. It is 
