232 BRITISH AVONIAN CONODONT FAUNAS 
Spathognathodus scitulus (Hinde) 
Plate 8, figs. ga—r1d 
1900 Polygnathus scitulus Hinde : 343, Pl. 9, figs. 9-11 only. 
1928 Panderodella scitula (Hinde) Holmes : 16, Pl. 6, figs. 26, 28 only. 
1960 Spathognathodus scitulus (Hinde) Clarke : 21, Pl. 3, figs. 12, 13. 
1962 Spathognathodus scitulus (Hinde) Rexroad & Collinson : 20, Pl. 2, figs. 14, 19, 29-31. 
MATERIAL. Ig specimens : figured, X 391, X 392, X 393. 
RANGE. North Crop CYD 6-3D 14/15, Avon Gorge C 15-D 27. 
DeEscriPTION. This spathognathodid is characterized by having an oral outline 
that is straight in the mid-third, but which plunges steeply towards the posterior end. 
It has relatively few denticles on the oral edge and a widely flared, arched, basal 
cavity on the outer lateral face. The posterior end is shallow and pointed. 
This short spathognathodid has a prominent plough-like antero-aboral area which 
may sometimes develop an irregular anterior edge. The antero-aboral margin is 
acute and more or less pointed and its posterior edge is feebly convex. The anterior 
edge of the unit is generally straight. The oral edge bears g denticles, which stand 
more or less erect to the general line of the blade, only their apices being discrete. 
The denticles decrease regularly in size towards the posterior end of the unit, the 
posterior 2 or 3 tending to be minute in size. The anterior denticle is much the 
largest, but the subsequent 4 or 5 denticles tend to be of rather uniform size, and the 
mid-third of the unit has a rather straight lateral edge. In outer lateral view, the 
sharp flexure of the unit and the widely flared basal cavity are prominent features. 
The posterior end of the unit is very shallow. The aboral edge is continuously 
concave and the posterior edge is bluntly pointed. The basal cavity itself is confined 
to the mid-third of the unit and it is flared only on the outer lateral side, the inner 
side being straight. 
Spathognathodus scitulus subsp. nov. A 
Plate 31, figs. 12a—c 
MATERIAL. 3 Specimens : X 390 (figured). 
RANGE. Scotland DUN 78. 
DEscrRIPTION. A Sphathognathodus scitulus with one or two inconspicuous 
accessory denticles developed on the anterior edge of the main denticle. 
The present specimens agree with typical individuals of S. scitulus (e.g. those 
illustrated by Rexroad & Collinson 1963, and Clarke 1960) except that the “‘ cusp ” 
(the most anterior denticle of the blade) has two small confluent denticles on its 
anterior aboral edge, which are developed parallel to the anterior margin. The 
denticles posterior to the main denticle, the general form of the blade, and the 
general structure and asymmetry of the basal cavity are otherwise similar to those 
of Spathognathodus scitulus s.s. 
