156 MAURICE G. MEHL 



anterior and posterior cutting edges. In the former genus, on the 

 other hand, as shown by Dr. E. Fraas,^ all the teeth are circular in 

 section. In Angistorhinus the anterior end of the rostrum is much 

 more abruptly down-turned and the downward extent is consider- 

 ably greater than in Mystriosuchus. In the former genus, too, the 

 posterior palatine foramina are much longer and more slit-like. In 

 a lateral view the cranium proper of Angistorhinus is seen to make 

 up a greater portion of the entire length of the, skull than is the case 

 in Mystriosuchus. 



Rutiodon, of which R. carolinensis is the type, probably resembles 

 Angistorhinus in general form more than any of the other genera. 

 The differences found in the vertebrae have been pointed out above 

 and it was shown that those of Angistorhinus were considerably the 

 larger. The skulls, too, beat out this difference in size. The total 

 length has not been determined for Rutiodon but the indications 

 are that it was about that of Mystriosuchus, viz., 820 mm.,^ while 

 that of Angistorhinus is from 977 mm. to 985 mm. or more. The 

 distance from the anterior border of the nares to the tip of the ros- 

 trum in the former is 510 mm.; in the latter genus the same meas- 

 urement is 590 mm. Although a direct comparison of the dentition 

 of the two forms is impossible, the teeth of Rutiodon at the middle 

 of the rostrum seem to be considerably larger than those of Angis- 

 torhinus. The post-temporal arcade of the latter is greatly devel- 

 oped (in this it seems to dififer from all other genera except perhaps 

 Palaeorhinus) and the posterior palatine foramina are quite differ- 

 ent. In the former genus they are almost round and probably not 

 over 15 mm. in diameter, while in Angistorhinus they are about 

 60 mm. long and about 8 mm. in diameter. 



Besides the much more anterior position of the nares in Palaeo- 

 rhinus and the but slightly down-curved tip of the rostrum, this 

 form differs from Angistorhinus in that the skull is much smaller 

 and the slender rostrum makes up but about one-half the entire 

 length. Palaeorhinus also has a less backward extension of the 

 upper posterior border of the skull, much less developed "squamosal 

 hooks," and the opisthotics are less massive, thinner, and more 

 spatulaform than in Angistorhinus. The anterior extent of the 



' Op. cit., p. 16. ^ McGregor, op. cit., p. 58. 



