84 BRITISH AVONIAN CONODONT FAUNAS 
by Dr. Rexroad as C. naviculus. We suspect that C. unicornis may be synonymous 
with C. naviculus. 
Cavusgnathus ? sp. nov. A 
Plate 9, figs. 1oa-d 
MATERIAL. 2 Specimens: figured, X 70. 
LOCALITY AND HORIZON. North Crop, ZLA 32. 
RANGE. North Crop ZLA 32. 
DEscrRIPTION. A cavusgnathid with the anterior blade developed on the left side 
when viewed from the posterior. 
The unit is highly reminiscent of species referable to the genus Cavusgnathus but 
the free blade is developed on the opposite side, that is, the left side, when viewed 
from the posterior. The platform is long, sinuous and deep, being ornamented by 
transverse ridges which become obsolescent towards the deep median trough. The 
trough is sinuous, deep, deepening towards the anterior, with a suggestion of a carina 
filling it near the posterior termination. The blade is broken, but can be seen to be 
situated on the opposite side of the platform to known cavusgnathids ; it appears to 
be high and formed of laterally compressed denticles. 
In aboral view the basal cavity occupies the whole platform area, the lips being 
flared, especially on the blade side, and on the posterior part of the non-bladed side. 
REMARKS. All known species of Cavusgnathus are asymmetrical units, the lateral 
blade being found on one side only and no mirror images being known (Rexroad 
in Lindstrém 1964 : 124). The above form is, in fact, a mirror image of a typical 
individual of the genus Cavusgnathus. 
Genus CLYDAGNATHUS gen. nov. 
DERIVATION OF NAME. From the River Clydach. 
Diacnosis. A lanceolate, curved platform unit, with short anterior blade, an 
elongate platform and medial trough. The blade is medial to lateral ; the platform 
is ornamented and may bear a posteriorly restricted carina ; basal cavity asym- 
metrical. The phylogenetic origin and stratigraphic range are described below 
(p. 85). 
TYPE SPECIES. Clydagnathus cavusformis gen. et. sp. nov. 
DeEscrIPTION. The blade is medial to lateral, short, and slopes anteriorly. The 
platform is lanceolate, elongated, bowed and laterally curved. It bears variable 
marginal ornament, ranging from nodes to transverse ridges. A medial trough is 
present, except at the posterior end, where a short medial carina is sometimes present 
which occasionally extends beyond the platform as a posterior blade. The asymmet- 
trical cavity is expanded, but is medially situated beneath the platform. The unit 
is not grooved. 
REMARKS. This genus is closely allied to Scaphignathus and Cavusgnathus. 
