THE UPPER TRIASSIC OF WESTERN TEXAS. 57 



IS complete and on a level with the roof of the skull; the interpterygoid vacuity is 

 rela ively large and the parasphenoid process is long, reaching to the anterior end of the 

 vacuity. The two forins differ in that in Angistorhinus the squamosals are much larger 

 and extend well beyond the occipital condyle, so that it is not visible from above- there 

 is a much sharper depression of the rostrum anterior to the external nares; the anterior 

 W M t^ '*''?""' '' more down-turned and is wider; the pterygoid is represented 



by Mehl as havmg no external process and the transverse joins it laterally, not by 

 underlying an externa process; the posterior arm of the parietal is short, the greater part 

 of the upper edge of the posterior part of the skull being formed by the squamosal; the 

 opisthotic process extends out to the squamosal, but is surrounded by it both above and 

 externally; the post-temporal foramen is relatively large. 



Comparison with Paleorhinus.' 



If Huene's suggestion of the phylogentic value of the relative position of the externa 

 nares and the antorbital vacuity is correct, Paleorhmus retains the primitive character 

 in a marked degree, for the antorbital vacuity is entirely posterior to the nares and has a 

 rounded anterior outline, indicating a very different form of the jaw-muscle; the squa- 

 mosal has a very large extension behind the occipital condyle. The proportion between 

 the relative lengths of the prenarial and postnarial portions of the skull is as 8 : 8.8, 

 or nearly as 1 : 1, approaching in this the probable condition in Mesorhinus. On the 

 other hand, the specialized character of the skull appears in the depression of the 

 parieto-squamosal arch, the shortness of the posterior bar of the parietal, the elevated 

 rim of the external nares, the position of the internal nares posterior to the external, 

 the small interpterygoid vacuity and the short parasphenoid, the strong external process 

 of the pterygoid with the transverse articulating with its lower surface, and the position 

 of the palatine vacuity anterior to the middle of the transverse. The characters de- 

 scribed by Lees^ of the elongate vomers reaching back to take part in the anterior edge 

 of the interpterygoid vacuity, the otic foramen between the squamosal and the quad- 

 ratojugal, and the position of the quadrate foramen on the lateral surface of the skull 

 have all been questioned by Mehl and Huene' and are so unHke the normal characters 

 of the other Parasuchia that they can not be accepted or discussed until the skull is 

 reexamined. The improbability of the existence of an otic foramen in the position de- 

 scribed by Lees is further emphasized by the discovery of the stapes in the normal position 

 of the lower side of the opisthotic in Promystriosuchus. 



Comparison with Mystriosuchus. 



This comparison is based on the published descriptions of Mystriosuchus planirostris 

 and M. pleiningeri by McGregor and Huene.* 



The lengths of the prenarial and postnarial portions of the skull of Mystriosuchus 

 are very closely as 5 : 2; the antorbital openings are elongate and extend forward either 

 to the anterior end of the nares {-planirostris) or slightly anterior to them {pleiningeri) ; 

 the nasal septum reaches the level of the skull; the parietals have no posterior bar 

 defining the inner side of the supratemporal opening; the parietals descend to the top 



' Williston, S. W., Journal of Geology, vol. xii, p. 696, 1904; Lees, J. H., Journal of Geology, vol. xv. No. 2, 



p. 121, 1907. 

 ^ Lees, J. H., The Skull of Paleorhinus, Journal of Geology, vol. xv, No. 2, p. 133, 1907. 

 ' Mehl, M. G., Journal of Geology, vol. xxiii, No. 2, p. 157, 1915; Huene, F. v., Neues Jahrb. f. Min. Geol. 



u. Pal., No. 19, p. 587, 1909. 

 * McGregor, J. H., Memoirs American Museum Natural History, vol. ix, pt. ii, 1906; Huene, F. v., Geolog- 



ische u. Paleontologische Abhandlungen, N. F., Bd. x, Hft. 1, p. 68, 1911. 



