BRITISH AVONIAN CONODONT FAUNAS 155 
1928 Lonchodus convexus (Hinde) Holmes (partim) : 14, Pl. 6, fig. 13. 
1931 Prioniodus bidentatus Gunnell 247, Pl. 29, fig. 6. 
1933 Prioniodus dactylodus Gunnell 265, Pl. 31, fig. 1. 
1941 Metalonchodina bidentata (Gunnell) Branson & Mehl: 106, Pl. 19, fig. 34. 
1941 Metalognathus bidentata (Gunnell) Ellison : 116, Pl. 20, figs. 35, 36. 
1952  Metalognathus bidentata (Gunnell) Rhodes : 898, Pl. 128 ‘m’. 
1957 Metalonchodina bidentata (Gunnell) Bischoff : 37, Pl. 5, figs. 13, 15, 46. 
1960 Metalonchodina conflecta Clarke : 17, Pl. 2, fig. 14. 
1961 Metalonchodina bidentata (Branson & Mehl) Higgins: PI. 12, fig. 9. 
1962 Metalonchodina bidentata (Gunnell) Higgins : Pl. 1, fig. 3. 
1964 Lonchodina ? nipponica Igo & Koike : 186, Pl. 27, fig. 20. 
1964 Metalonchodina sp. Rexroad & Furnish : 673, Pl. 111, fig. 7. 
1965 Metalonchodina fragilis Murray & Chronic : 605, Pl. 73, figs. 19, 20. 
Metalonchodina bidentata (Gunnell) Collinson & Druce (in press). 
MATERIAL. 6 specimens : figured, X 253, X 254, X 255, X 256. 
RANGE. North Crop 3D 10-3D 14/15. 
DeEscriPTION. The present specimens agree closely with Branson & Mehl’s 
(1941 : 106) definition of the species. The anterior limb is shorter than the posterior 
bar and bears a massive denticle or pair of denticles upon it. In aboral view the 
most conspicuous feature is the very strong lateral flexing below the apex of the two 
bars. The small and fairly shallow pit is situated in the middle of the strongly 
laterally expanded aboral surfaces at this point ; the aboral surfaces of each limb 
being relatively flat or obtusely V-shaped. They are excavated by very narrow 
shallow slit-like cavities along their lengths. The chief expansion of the base below 
the apical denticle is concentrated on the inner lateral side and is a very prominent 
feature of the unit. In inner lateral view the most conspicuous feature of the unit is 
the enormous size of the denticle developed on the anterior bar. This is about two 
to three times as wide as any of the other denticles, has straight anterior and posterior 
edges and is bluntly pointed. It has gently convex inner and outer lateral faces. 
The anterior edge of the unit is developed into a triangular pointed anterior end. Its 
aboral margin is straight, and although its junction with the posterior bar is curved, 
it makes an angle of 80°-g0° with the aboral surface of the latter. The posterior bar 
bears two or three smaller denticles, sub-circular in cross-section, with inconspicuous 
anterior and posterior edges, which are inclined anteriorly. 
Apical denticle 
7 ain denticie 
Inner lateral 
aboral expansion Anterior limb 
Posterior bor 
Aboral margin 
Fic. 31. Metalonchodina sp. showing morphological terms used in the text. 
