THE UPPER TRIASSIC OF WESTERN TEXAS. 63 



the jugal is deeply dovetailed into it. This method of articulation is confirmed by its 

 presence in two specimens in the University of Michigan collection. The jugal is visible 

 along the lower edge of the skull to the posterior end of the quadrate. 



The quadratojugal is a nearly triangular plate which covers the outer side of the 

 quadrate almost entirely and takes slight part in the formation of the posterior edge of 

 the lateral temporal fenestra. 



The quadrate appears on the side of the skull only at the posterior lower corner and 

 as a thin edge at the posterior line of the skull. 



The squamosal has a very large lateral presentation and a correspondingly small 

 presentation on the upper surface, apparently less than in any previously described form. 

 The lateral surface is nearly vertical; its posterior portion extends 52 mm. beyond the 

 end of the opisthotic, forming a very decided projection at the posterior end of the skull. 

 From the lower edge of this projecting portion there is a strong descending process, 

 the anterior edge of which forms the posterior border of the otic notch. Within the 

 notch the upper part of the quadrate and a portion of the distal end of the opisthotic 

 can be seen from the side. 



The posterior face of the skull. — This face of the skull is more distorted than any 

 other, due to the upward movement of the right side in the compression accompanying 

 fossilization. The occipital condyle is forced somewhat to the left and the bones above 

 the condyle are somewhat broken and displaced. It is, however, easy to restore the 

 original condition. 



The parietals descend very abruptly and lie upon the upper edge of the opisthotic. 

 The post-temporal opening was either entirely occluded or was represented by a small 

 opening not greater than a large foramen. The outer edge of the parietal articulates 

 with the anterior edge of the process described on the inner side of the squamosal. 



The supraoccipital is a small triangular bone which in the specimen is separate 

 from the exoccipital-opisthotic on the left side, so that the outline is plain. 



The exoccipitals are separated from the basioccipital by distinct sutures, but are 

 still in position. The lower portions meet in the median line, excluding the basioccipital 

 from any part in the floor of the foramen mangum, at least its posterior part. There 

 is no suture visible between the exoccipitals and the opisthotics. 



The opisthotics are expanded at the inner end, where they contain a portion of 

 the cavity of the inner ear. Beyond the exoccipital portion they contract rapidly, and 

 the outer half is spatulate in form, with the outer end reaching to the extreme outer 

 edge of the squamosal, but, in the specimen, not visible in a lateral view of the skull. 

 The lower edge of the inner third is marked by a distinct groove, which evidently 

 protected the stapes in part. This groove becomes deeper toward the inner end and 

 is continued on the lower edge of the prootic. 



The squamosals. — The inner side of the squamosal is best seen from the posterior 

 surface. This face is nearly vertical, but is divided by a horizontal ridge which originates 

 near the posterior end and, growing more prominent as it advances, terminates near the 

 middle of the length of the squamosal. To the anterior end of this ridge is articulated 

 the distal end of the parietal. Immediately below the ridge lies the distal end of the 

 opisthotic, which is here a narrow, oval plate with its greatest diameter nearly vertical. 

 The extremity of the opisthotic reaches nearly to the posterior end of the descending 

 process from the squamosal, but is not visible from the outer side. The upper outer 

 corner of the quadrate articulates with the squamosal by a rounded head just anterior 

 to the end of the ridge described on the inner surface of the squamosal. 



The quadrates. — These are much as described in other specimens. Each quadrate 

 stands upright in the skull, with a broad posterior face, which contracts toward its 



