BRITISH AVONIAN CONODONT FAUNAS 87 
penultimate posterior. The platform is ornamented by two rows of irregular nodes. 
The margins are separated by a shallow trough, which generally tends to close 
towards the anterior, and occasionally possess a short carina at the posterior 
extremity. The lateral denticles on the blade side of the platform tend to be rather 
larger than those on the other side. In smaller specimens, the basally confluent 
platform denticles have sharply pointed, discrete apices in lateral view, but they 
become more blunt in larger specimens. The platform walls are deep, and the aboral 
outline is straight over the anterior two-thirds, but the posterior one-third can be 
deflected downwards, especially in smaller specimens. 
In aboral view, the unit is excavated, the cavity being large, flaring and asym- 
metrical, extending from nearly the posterior extremity of the platform to its 
junction with the anterior blade. 
REMARKS. This species can be distinguished from all other clydagnathids by 
the character of the blade. 
Clydagnathus gilwernensis sp. nov. 
Plate 2, fig. ra—d 
DERIVATION OF NAME. From the locality at Gilwern. 
Dracnosis. Clydagnathid with short, high, medial, anterior blade, and short 
posterior carina occasionally developed into a short posterior blade. 
MATERIAL. 7 specimens : Holotype X 78 (figured). 
TYPE LOCALITY AND HORIZON. R. Clydach, Nr. Gilwern, K Zone. North Crop. 
Sample KL 1. 
Rance. North Crop KL 1-KL 6, Avon Gorge K 6. 
DEsScRIPTION. The anterior blade is short and situated medially. It commonly 
bears three denticles, the posteriormost being the tallest and most massive. The 
blade denticles, which have blunt or chevron tips, are laterally compressed, and are 
fused at their bases. They decrease rapidly in size anteriorly. The anterio-aboral 
portion of the blade is strongly protruding and bluntly spatulate in profile. The 
platform is long, slender and posteriorly sharply pointed ; it has two lateral rows of 
blunt, triangular lateral nodes, with a shallow medial trough which is filled at the 
posteriormost extremity by a short carina of 2 to 4 nodes, which may extend beyond 
the platform to give a short posterior blade. On some specimens the carina may be 
absent. 
In lateral view the posterior platform of young forms is “‘ upstepped ”’ relative to 
the blade, but in mature specimens the unit is arched about the cavity. 
In aboral view there is an asymmetrical medial cavity situated in the anterior 
third of the platform. It has longitudinally thickened lips ; a faint groove some- 
times runs a short distance either side of the cavity. 
REMARKS. In gross morphological terms C. gilwernensis is similar to Patrognathus 
variabilis but the vastly different cavity, the distinctive blade and excavated medial 
trough serve to distinguish it. It would appear that the two forms were the result 
