188 MAURICE G. MEHL 
squamosal of Mystriosuchus planirostris has an even greater 
development in this form. The hooklike process in A. grandis 
extends below the plane of the dorsal surface of the skull a distance 
of about 1o4 mm. Although all the teeth but the roots of the 
anterior ones have dropped from the alveoli, a fairly good idea of 
the dentition can be gained. The downward extension of the 
rostrum contains four teeth, sections of the roots of which show a 
diameter of about 15 mm. The anterior teeth of another specimen 
(described below), although of less diameter, reach a length of 
about 78 mm., a fact that would bespeak a still greater length for 
the anterior teeth of A. grandis. Sections through the rostrum dis- 
closed teeth that had not yet been erupted. These, as many others 
found loose in the matrix, were laterally compressed with anterior 
and posterior sharp, finely serrate, cutting edges. 
The differences between Angistorhinus and the forms that it 
resembles seem evident. From Mystriosuchus it differs in possession 
of laterally compressed posterior teeth with sharp, more or less 
serrate cutting edges. Quoting Dr. E. Fraas (op. cit., p. 16): 
“Die Zahne selbst sind auch nicht glatt und mit scharfer Kante 
versehen, sondern schwach gerieft und von rundem Querschnitt 
ohne Kante, sie gleichen am meisten den Nothosaurus-Zahnen aus 
den Bonebeds. Dass eine Species mit derartigen Zahnen nicht gut 
Belodon (Pfeilzahn) genannt werden kan, wird man mir zugaben.”’ 
McGregor has characterized not only Mystriosuchus, but the 
entire suborder, Phytosauria, as having the parieto-squamosal 
arcade greatly reduced and depressed.t In Angistorhinus this is 
decidedly not the case; the arcade is well developed and lies in the 
plane of the posterior dorsal surface of the skull. 
From Rhytidodon carolinensis Emmons? Angistorhinus difiers 
considerably in the development and position of the parieto- 
squamosal arcade, for Rhytidodon and Mystriosuchus seem to be 
very similar in this respect. To quote Dr. McGregor (op. cit., p. 
* Memoirs of the Amer. Mus. of Nat. Hist., TX, Part II (1896), 92. 
2 This is the genus and species recognized by McGregor (ibid., p. 95). F. von 
Huene (Beitrage zur Kenntnis und Beurteilung der Parasuchier, 1911, p. 42) has included 
Rhytidodon in the genus Mystriosuchus, but Emmons’ genus seems to stand, as the 
teeth are shown by McGregor to be laterally compressed, some with cutting edges, 
whereas, as pointed out above, the teeth in Mystriosuchus are all round in cross-section. 
