THE PHYTOSAURIA OF THE TRIAS 157 



pre- and parasphenoid and of the inter-pterygoid vacuity is appar- 

 ently considerably less in the former genus, and the pterygoid 

 process of the basisphenoid is less massive and more separated from 

 the greater wings than in the latter. The number of teeth in the 

 upper mandible of Palaeorhinus is about 72, while in Angistorhinus 

 they number 84. In all probability the post-temporal arcade is 

 somewhat the same in both forms. Of this more will be said later 

 in the special reference to Palaeorhinus. 



The anterior part of the rostrum of Mesorhinus fraasi is missing. 

 The rostrum therefore affords little material for comparison. What 

 remains of it, however, suggests a form between Angistorhinus and 

 Lophoprosopus. The external nares are much more anterior in 

 Mesorhinus than in Angistorhinus, and the former, according to 

 Jaekel, possess a parietal foramen. There is also apparently a 

 difference in the elements about the anterior border of the nares 

 in the two forms. Jaekel says:^ 



Zwischen den vordern Enden der Nasenlocher stehen zwei vertikale 

 schmale Knochenleisten, die ich unbedenklich als Telle der Pramaxillaris 

 angesprochen haben wiirde, wenn nicht Herr v. Huene ahnliche Gebilde bei 

 anderen Belodonten eben als besondere Elemente, als Septomaxillaria beschrie- 

 ben hatte. 



F. von Huene, however, in a later paper, considers these as the 

 ends of the premaxillae.^ If we accept the interpretation of the 

 latter, the difference between the two forms in this respect is evi- 

 dent. In Angistorhinus the septomaxillary bones seem to unite in 

 the median Hne in front of the nares and exclude the premaxillae 

 from that opening, while the premaxillae of Mesorhinus supposedly 

 form the anterior and much of the lateral borders of the nares. 

 While the parieto-squamosal arcade seems to be developed some- 

 what similar in the two forms, if one may judge from the figures of 

 Mesorhinus, its posterior extent is not so great in the latter. 



Palaeorhinus bransoni Williston 



This genus and species was briefly described by Dr. S. W. 

 Williston in 1904.^ In 1907, after a detailed study of the type 

 specimen, Mr. J. H. Lees published a much fuller description of 



^ op. cit., p. 201. 2 Op. cit., p. so. i Jour. Geo!., XII (1904), p. 696. 



