THE UPPER TRIASSIC OF WESTERN TEXAS. 49 



A NEW PARASUCHIAN, PROMYSTRIOSUCHUS EHLERSI. 



The specimen (No. 7487, University of Michigan) described below was discovered 

 by the author in a bed of yellowish sandy clay near the head of Holmes Creek, Crosby 

 County, Texas, in the summer of 1921. The patch of sandy clay is but a minor phase 

 of the larger deposit in which so many remains of reptiles and amphibians occur in this 

 locality. Near the specimen, and in the same kind of matrix, occur large numbers of 

 fragmentary bones, teeth, and coprolites. This small patch is evidently a bit of an old 

 sand-bar, or an accumulation of sandy clay in some small depression which has been 

 well leached by percolating waters. The relatively small percentage of clay rendered 

 the matrix easily permeable by the waters which converted the iron into limonite and in 

 spots removed it so completely that the matrix is pure white; in other spots the matrix 

 is still purple from the unchanged iron of the original deposit. The limonite was con- 

 centrated upon the bones, covering them with a thin scale, and was deposited in the 

 cracks between the pieces of the broken bones. Movements in the ground crushed the 

 skull and broke it into many small pieces which are slightly displaced. The cleaning 

 and restoration were rendered difficult by the distortion and breaking of the bones, but 

 as the fragments were only slightly displaced it was possible to harden the matrix or 

 replace it by plaster cement and work out the original form of the skull. The anterior 

 half of the long rostrum was weathered out, but it has been possible to fit the pieces into 

 place and determine very accurately the length and form of the nose. From the narial 

 opening forward, the two halves of the skull were separated slightly; the palate was 

 crushed and pushed somewhat toward the left side. The posterior part of the lower jaw 

 of the left side was recovered, but the anterior end was destroyed by decay before 

 fossilization. 



Because of the fractured and compressed condition of the skull, it is intelligible 

 only after considerable study; the figures presented are restorations which have been 

 made with as great accuracy as possible, being the result of six different attempts, made 

 as checks, and are, in the opinion of the author, very satisfactory representations of the 

 original condition. The location of the sutures was rendered difficult by the innumerable 

 cracks and the condition of the specimen; only those that have been determined with 

 certainty are represented in solid line. 



The peculiar characteristics of the specimen are the slight extension of the squamosal 

 region behind the occipital condyle, the elevated position of the parieto-squamosal arch, 

 the absence or small size of the post-temporal opening, the very long parasphenoid 

 process, and the large interpterygoid space. The lack of any great posterior extension 

 of the squamosal region, the great length of the parasphenoid, and the large interpterygoid 

 space are primitive characters recalling the condition in Mesorhinus, but the development 

 of the external process of the pterygoids, the character of the transverse, the shape and 

 condition of the palatines, and the elongate rostrum are features belonging to the more 

 highly specialized of the Phytosaurs of the Upper Triassic. The suggestion of immaturity 

 conveyed by the small size of the skull is not borne out by the condition of the bones 

 and the sutures. It is evident that we have to do with a fully mature Phytosaur of the 

 Mystriosuchid group, of small size and distinct in its characters from any previously 

 described. 



The upper surface of the skull (plate 11, fig. a). — The openings in the skull: The 

 supratemporal openings are elongate oval and lie entirely upon the upper surface of the 

 skull; their boundaries are shown in the figures. The orbits are somewhat oval in outline 

 and lie almost entirely upon the surface; the lateral presentation is very slight. The 

 narial opening is entirely upon the upper surface and is surrounded by an elevated 

 rim; it is divided somewhat deeply below the rim by a pair of small bones which are 



