234 BRITISH AVONIAN CONODONT FAUNAS 
MATERIAL. 387 specimens : figured, X 554—X 557. 
RANGE. North Crop ZLA 2-ZLA 33, Avon Gorge Z 35-D 27. 
DESCRIPTION. This species is a simple denticulate unit bearing a regular succes- 
sion of denticles which decrease in height from anterior to posterior. The anterior 
denticle tends to be massive, taller and nearly twice as wide as the remainder ; the 
next two denticles in a posterior direction tend to be fairly narrow and fused ; the 
remainder have free chevron-shaped tips and are slightly larger. 
In aboral view the cavity is large with some flaring of the lips ; it begins imme- 
diately posterior to the anterior denticle and runs to the posterior termination of the 
unit. The lips are arched anteriorly and the whole cavity is symmetrical. 
REMARKS. This form agrees very closely with S. cristulus (Youngquist & Miller, 
1949 : 621, Pl. rot, figs. 1-3), except that their specimens commonly have Io smaller 
denticles, whereas the present forms have from 7 to 16 denticles. They agree 
exactly with a form included in S. regularis (Branson & Mehl 1938A), even to the 
number of denticles. Branson & Mehl, and Rexroad & Scott (1964 : 50) recognize 
forms with one major anterior denticle within the specific terms of S. regularis, but 
since our fauna contains specimens with only one major denticle, and no specimens 
with the two anterior denticles typical of the holotype of S. vegularis, there are 
obviously two separate species involved. The present specimens are compared to 
S. cristulus because of their close resemblance, but they are stratigraphically younger 
and may be a separate, perhaps ancestral, species. 
Spathognathodus cf. cyrius (Cooper) 
Plate 7, figs. 12a-14c 
1939 Spathodus sulciferus Branson & Mehl ; Cooper (partim) : Pl. 45, fig. 17, (non PI. 
45, fig. 18 = S. crassidentatus). 
1939 Spathodus cyrius Cooper : 413, Pl. 45, fig. 25. 
non 1943 Spathognathodus cyvius (Cooper) Cooper & Sloss: 175, Pl. 28, figs. 3, 4, Io, 12 
(= S. crassidentatus). 
1951 Spathognathodus macey Branson & Mehl; Youngquist & Downs: 791, Pl. 111, 
HieSy 2 
MATERIAL. Ig specimens : figured, X 470, X 469, X 471. 
RANGE. North Crop KL 2-ZLA 2, Avon Gorge Z 1-Z 13. 
DescriPTION. This is a simple arched and bowed unit which is highest at the 
anterior end ; the anterior part consists of 3 high denticles with the medial one the 
largest. The rest of the unit is made up of lower denticles, the medial part consisting 
of denticles of equal height and the posterior part shallowing with progressively 
smaller denticles. In the medial part the denticles are very fine and fused, 2 denticles 
commonly having only one emergent oral extremity. The unit commonly bears, 
besides the large anterior denticles, 30 smaller denticles. 
The cavity is situated medially and is relatively small and pear-shaped. 
