78 MESSES. HANCOCK AND ATTHEY ON 



which we have called the cranial shield, though the curves are 

 more flowing. But the parietals differ considerably in shape : 

 in Loxomma they appear to be simply elongated, and scarcely, 

 if at all, enlarged behind ;* while in Pterojdax they are much 

 enlarged posteriorly, and the frontals seem to be more produced. 

 The sternal plates likewise differ from those of Prof. Huxley's 

 genus, in which the lateral ones are quite short ; but in Pterop- 

 lax they are much elongated, agreeing in this respect with Ar- 

 chegosaurus ; and the central plate in Loxomma is devoid of the 

 remarkable lateral lobes which characterize that of our genus. 



We have also seen that this new reptile resembles to some 

 extent Basyceps, particularly in the two occipital horns ; but the 

 small eyes, backward position of the parietal foramen and exter- 

 nal nostrils, and the difference in the form of the cranial bones, 

 as well as the smallness and different character of the teeth of 

 that genus, sufficiently distinguish it from Pteroplax. 



This new genus is also related to Antliracosaurus, as is appar- 

 ent by the similarity of the vertebrae, the only difference of im- 

 portance being that in this new Labyrinthodont there is a minute 

 notochord, while the centrum of Antliracosaurus is completely 

 ossified, and the neural arch of the former is oval instead of 

 being triangular as it is in the latter. The occipital region, also, 

 in the two forms is very different : and the teeth disagree both 

 in form and minute structure ; indeed, the strongly compressed 

 crown, with its wide cutting edges, seems very characteristic in 

 Pteroplax cornuta. 



When the tooth is seen in transverse section converging spaces 

 are observed dividing the internal vertical folds or plicae of den- 

 tine : these spaces are widest towards the periphery of the tooth, 

 and are nearly all lost before they reach the pulp cavity, the 

 plicse having coalesced at their internal extremities.! The pKcae 

 are much undulated or lobulated, and have, extending through 



♦"Proceedings" Geological Society, Vol. XVIII., p. 292, Plate XI. 



t Since the above was in print we have examined other sections of the tooth, and find that 

 the radial spaces dividing the plicse of dentine are occasionally continuous with the pulp 

 cavity ; it would therefore seem that in the minute structure the tooth differs less from that 

 of Anthracosattrtis than we supposed. 



