BRITISH AVONIAN CONODONT FAUNAS 227 
1939 Spathodus crassidentatus Branson & Mehl ; Cooper: 413, Pl. 45, fig. 19. 
1939 Spathodus aciedentatus E. R. Branson ; Cooper: 413, Pl. 45, figs. 26, 28, 44. 
1939 Spathodus chouteauensis Cooper : 413, Pl. 45, fig. 20. 
1939 Spathodus strigilis Huddle ; Cooper: 416, Pl. 45, fig. 37. 
1939 Spathodus sulciferus Branson & Mehl ; Cooper (partim) : 416, 420, Pl. 45, fig. 18. 
1939 Spathodus isus Cooper : 413, Pl. 45, fig. 33. 
1943 Spathodus strigilis Huddle ; Cooper & Sloss : 175, Pl. 28, figs. 3, 4, Io, 12. 
1943 Spathognathodus crassidentatus (Branson & Mehl) Cooper & Sloss : 175, Pl. 28, fig. 1. 
1949 Spathognathodus crassidentatus (Branson & Mehl) Youngquist & Patterson : 71, Pl. 15, 
fig. 2. 
1949 Spathognathodus aciedentatus (E. R. Branson) Youngquist & Patterson : 71, Pl. 15, fig. 3. 
1949 Spathognathodus quintidentatus Thomas : 429, Pl. 4, figs. 8, 9. 
1949 Spathognathodus aciedentatus (E. R. Branson) Thomas, Pl. 4, fig. 7. 
1956 Spathognathodus crassidentatus (Branson & Mehl) Bischoff & Ziegler (partim) : 166, 
Pl. 13, fig. 14 (non Pl. 13, fig. 13). 
1957 Spathognathodus crassidentatus (Branson & Mehl) Bischoff : 56. 
1961 Spathognathodus crassidentatus (Branson & Mehl) Freyer : 85, Pl. 6, fig. 138. 
1964 Spathognathodus crassidentatus (Branson & Mehl) Rexroad & Scott: 48, Pl. 3, figs. 7, 
8. 
MATERIAL. 222 specimens : figured, X 460, X 461, X 462, X 463. 
RANGE. North Crop KL 2-ZLA 33, Avon Gorge K 17-Z 38. 
DESCRIPTION. This is a simple arched and bowed unit, which is highest at the 
anterior. The anterior blade consists of 3 to 6 tall, massive denticles which are 
basally confluent, with discrete blunt apices, the denticles in the medial part of the 
blade being highest. The mid-third of the unit consists of denticles of even height, 
conspicuously lower than the anterior denticles. The denticles of the posterior third 
decrease in height towards the posterior termination. The total number of denticles 
ranges from 17 to 22. 
In aboral view a large cavity, situated medially, is symmetrically flared and widest 
just anterior to its mid-point. The cavity is extended both anteriorly and posteriorly 
as a narrowing groove, the posterior extension being the longer. 
REMARKS. This species is common, and, as was pointed out by Rexroad and Scott 
(1964 : 49), is highly variable. Although we accept most of the synonomy of those 
authors, we believe that forms with a very much greater denticle density should not 
be included under S. crassidentatus, but should be referred to S. cyrius (Cooper) (see 
Pp. 234). 
Spathognathodus cristulus Youngquist & Miller 
Plate 8, figs. 14a—18d 
1949 Spathognathodus cristula Youngquist & Miller : 621, Pl. rot, figs. 1-3. 
1957 Spathognathodus cristula Youngquist & Miller ; Rexroad : 38, Pl. 3, figs. 16, 17. 
1958 Spathognathodus cristula Youngquist & Miller ; Rexroad : 25, Pl. 6, figs. 3, 4. 
T961 Spathognathodus cristula Youngquist & Miller; Rexroad & Burton: 1156, Pl. 141, 
fig. 9. 
1962 Spathognathodus cristula Youngquist & Miller ; Rexroad & Liebe : 511, table 1. 
1964 Spathognathodus cristula Youngquist & Miller; Rexroad & Furnish: 674, Pl. 111, 
fig. 15. 
1965 Spathognathodus cristula Youngquist & Miller ; Rexroad & Nicoll: 26, Pl. 1, figs. 1, 2. 
