144 BRITISH AVONIAN CONODONT FAUNAS 
to be rather straight, but are discrete, sharply pointed, and tend to be directed 
inwardly, being either erect to the posterior bar or in a few cases sloping slightly 
forward ; in most specimens, however, they are either erect or posteriorly inclined. 
The posterior denticles tend to decrease in size posteriorly. 
The basal cavity is strongly developed on the inner side of the unit, but it is wide, 
rather than deep ; it extends as a very narrow groove along the bars. 
Lonchodina transitans Collinson & Druce 
Plate 31, fig. 14 
Lonchodina transitans Collinson & Druce (in press). 
MATERIAL. 3 specimens : figured, X 234. 
RANGE. North Crop 3D 4-3D 14/15. 
DEscRIPTION. The present specimens are incomplete but they show the essential 
features of the species, including the angle of divergence of the anterior and posterior 
bars of about 130° and the more or less bilaterally asymmetrical open “ ligonodina ”’ 
type cavity which is developed below the apical denticle. The apical denticle is 
recurved and relatively slender. The posterior bar is broken in the present speci- 
mens but bears at least 2 discrete, sharply pointed, posteriorly inclined denticles. The 
anterior bar is straight, and is slightly inflexed, as well as being depressed ; it bears 
at least 3 laterally compressed, recurved, slightly incurved denticles. Both bars are 
excavated by aboral grooves which extend into the shallow and rather flared cavity 
below the basal surface of the apical denticle. The apical denticle is biconvex in 
cross-section in its proximal part, and its strong lateral expansion on the outer face 
develops a suggestion of a median ridge on the lower part of that surface. 
RemaARKs. Collinson & Druce have pointed out that this species represents a 
transitional form between the genera Ligonodina and Lonchodina. 
Lonchodina sp. A 
Plate 24, figs. 17a, b 
MATERIAL. 6 specimens : figured, X 424. 
RANGE. North Crop ZLA 32-ZLA 33. 
DeEscRIPTION. All the present specimens are broken, but they appear to represent 
a short unit, the bars being restricted. The apical denticle is large, laterally com- 
pressed and inclined toward the inner side. The bars appear to be curved on the 
outer side. The basal cavity is large and occurs beneath the apical denticle. 
Genus MAGNILATERELLA Rexroad & Collinson 1963 
1963 Magnilaterella Rexroad & Collinson : It. 
Type SPECIES. Magnilaterella robusta Rexroad & Collinson 1963. 
