152 BRITISH AVONIAN CONODONT FAUNAS 
The basal surface is characterized by a restricted median cavity, which is shallow 
and occupies the anterior half of the platform. It extends anteriorly and posteriorly 
as a very narrow shallow slit along the unit. 
Mestognathus bipluti Higgins 
Plate 25, figs. ra—3c, 8a, b 
1961 Mestognathus bipluti Higgins : 216, Pl. ro, figs. 1, 2; text-fig. 4. 
DiaGnosis. This species is characterized by a short, deep blade which diverges at 
the anterior end of the unit from the antero-inner lateral edge of the platform. 
Slender and pointed platform has a more or less prominent median carina. 
MATERIAL. 3 specimens : figured, X 249, X 248, X 246, X 247. 
Rance. North Crop CYD 6-CYD 7. 
DESCRIPTION. This species of conodont has an outline that is reminiscent to some 
extent of a folsom-point. The inner edge of the platform is straight in the anterior 
two thirds and then turns rapidly inwards towards the pointed posterior end. The 
posterior third is also straight and the bend is sharply angular. The outer lateral 
margin of the platform is straight in its anterior third and up to the end of the 
anterior blade, but posteriorly it is turned sharply inwards towards the pointed 
posterior end. The posterior outer lateral face is more or less straight. There is a 
strongly developed posterior carina, which consists of a series of confluent nodes, and 
extends about half the length of the platform. It is continued less obviously 
anteriorly to meet the antero-inner lateral point as a low inconspicuous ridge. There 
is a narrow deep trough adjacent to the blade and this becomes shallower and 
obsolescent posteriorly, extending on the outer side of the median carina. The inner 
lateral portion of the platform adjacent to the carina tends to be flat or feebly con- 
cave. The margins of the platform are ornamented by relatively strongly developed 
transverse ridges, which tend to become less conspicuous towards the posterior end. 
They extend about half the distance from the lateral margins to the carina. The 
lateral margins themselves are gently up-flexed. The downward and outward 
curvature of the antero-aboral portion of the blade is a conspicuous feature in oral 
view, as is the divergence of the anterior blade and the antero-inner edge of the 
platform to give a branched structure. 
In aboral view this latter feature is the most conspicuous characteristic of the 
species. The total length of the branches are a third to a quarter of the length of the 
platform. The medial cavity is very small and inconspicuous and is only slightly 
flared. It extends anteriorly and posteriorly as a keeled narrow slit along the 
median line of the unit. The main cavity is situated near the junction of the blade. 
In inner lateral view the oral surface of the unit is bluntly serrated and the posterior 
end is bluntly spatulate. In outer lateral view the aboral margin is straight in 
the posterior half, but gently concave in the anterior half. In outer lateral view 
the anterior blade is a very distinctive feature. The posterior denticle is the largest 
and the blade decreases regularly in depth towards the bluntly spatulate anterior end. 
