54 



NEW REPTILES AND STEGOCEPHALIANS FROM 



nai 



FIG. 21. Promystrio- 

 suchus ehlersi. 



Median surface of the 

 narial region, left side. 

 na., nasal. X 0.6. 



which divides the nares some distance below the level of the rim. These bones are thin, 

 but nearly a centimeter in height on the broad inner surface, which was closely applied 

 to the bone of the opposite side. These are probably extensions of the nasals. On 

 the left side, in what is apparently a direct continuum with the median palatal element, 

 probably the palatine (vomer ?), there is a slender bar of bone distinct from both the 

 nasal and the premaxillary. As this bar is above the premaxillaries in the region where 

 they meet in the median line, it can not be a bar separating the internal nares; rather it 

 seems to be a bar vertically placed beneath the nasals and denning an opening which 

 permits the nasal to open laterally into passages which lead back to the somewhat 

 posteriorly placed internal nares. The separate character and 

 distinct identity of this bar is proven by the fact that it was 

 surrounded by matrix, which has penetrated between it and the 

 adjacent bones, and by its rounded edges revealed under the 

 binocular microscope. 



The posterior face of the skull (plate 11, fig. D). The crushing 

 of the skull has almost completely closed the foramen magnum, and 

 in the restoration allowance has been made for this depression as 

 accurately as possible. The sutures between the elements forming 

 the edges of the foramen magnum can not be made out. 



The basioccipital carries a good-sized, nearly hemispherical 

 condyle; the sides of the neck run forward and upward to join 

 the exoccipital-opisthotics. It has been impossible to determine 

 the position of any of the nerve outlets. 



The exoccipital and the opisthotic are closely fused; the opis- 

 thotic portion extends outward and backward at a fairly sharp angle; the outer portion 

 becomes thinned laterally, but retains its vertical extent; the outer end terminates freely 

 below the distal end of the squamosal. 



The supraoccipital is a rather broad plate inclined sharply forward in the median 

 line, but becoming more nearly vertical tow r ard the sides; it is closely attached to the 

 slender parietals above, which are visible only as thin edges from the rear. The post- 

 temporal openings are entirely closed, if they were present, which is quite probable. 

 An enlargement visible on the upper edge of the opisthotic in the usual position of the 

 openings may be due to crushing. Small post-temporal openings have been shown in 

 the restoration. 



The squamosal has a relatively small presentation on the posterior face of the skull ; 

 it sends a short prong inward between the distal end of the opisthotic and the supraoc- 

 cipital and a second one above the supraoccipital to unite with the parietal. Just above 

 the distal end of the opisthotic is the prominent posterior termination of the squamosal, 

 and below this is the small fragment of bone on the outer side of the opisthotic which 

 McGregor identified as a hyoid element in Mystriosuchus. Externally the squamosal 

 sends a strong process forward and outward to join the quadratojugal; the lower surface 

 is excavated for the reception of the upper end of the quadrate. 



The quadrate has a nearly quadrangular posterior surface. This surface inclines 

 inward and forward beneath the opisthotic; the upper half of the inner edge forms the 

 articulation for the pterygoid. The outer edge is covered by the quadratojugal, which 

 sends a short process around the outer edge on to the posterior face near the outer lower 

 corner. About midway up the outer edge there is a good-sized quadrate foramen 

 surrounded by the quadrate and quadratojugal. There is no indication that the quadrate 

 process of the pterygoid appeared on the outer face of the skull, as described by Huene 1 

 in Mystriosuchus pleiningeri. 



1 Huene, F. v., Geolog. u. Paleontolog. Abhdlg., N. F., Bd. x, Hft. 1, s. 81, 1911. 



