THE UPPER TRIASSIC OF WESTERN TEXAS. 61 



NEW PARASUCHIANS, LEPTOSUCHUS CROSBIENSIS AND LEPTO- 

 SUCHUS IMPERFECTA, FROM CROSBY COUNTY, TEXAS. 



The first skull (Leptosuchus crosbiensis, No. 7522, University of Michigan) is 

 singularly perfect. All of the bones except those of the posterior portion of the upper 

 surface are preserved in place and the loose ones were found close to the specimen. 

 One half of the lower jaw was found overlying the skull, and the posterior portion of the 

 other half was found not far distant. Total length of the skull, 87.5 cm. 



The second skull (No. 7523, University of Michigan) is much larger than the 

 first and was found entirely washed out and lying on the surface as a mass of fragments. 

 Some parte had disappeared and the skull as mounted is in part restored. Total length 

 as restored 112 cm. 



Skull No. 7522 is so singularly perfect that it warrants a rather full description. 

 It was completely covered when found, the removal of the half of the lower jaw over- 

 lying it leading to its discovery. The matrix is a fine yellowish clay broken into 

 innumerable small pieces, between which are sheets of calcite not over 0.1 mm. thick. 

 The skull is slightly compressed, the right side is a little displaced upward, and the bones 

 of the posterior portion are a little distorted. The extremely complex fracturing of the 

 matrix compelled a fracturing of the bone which is only slightly less in degree, but the 

 fragments are all in position. The skull was collected in a block of matrix and has been 

 prepared and mounted by the painstaking and skilful work of Mr. William H. Buettner. 



Particularly important is the preservation, in the natural position, of the extremely 

 thin bones of the palatal region. This permits a determination of the complete osteology 

 of the skull. 



The upper surface of the skull. — The best idea of the position and relation of the 

 bones may be gained from figure 25 a. The narrow upper surface of the squamosals is in 

 striking contrast with most other forms of the Phytosaurs. 



The lateral $urfaee »/ the skull. — Seen from the side, the premaxiliartee are similar 

 in form and relations to the same hones in the majority of the forms of the Mystriosuchid 

 group. The anterior end is sharply down-curved, with a decided notch behind the 

 prominent anterior tusks for the reception of the tusks of the lower jaw. Near the 

 middle of the bone there is a low but very evident prominence on the upper surface. 

 This seems to be a common and normal structure in most, if not all, of the Mystriosuchids. 

 It occurs in all the specimens preserved in the University of Michigan collection and is 

 figured and described by v. Huene in M. pleiningeri. Huene attributed the prominence 

 to an accident, but it is clear that it may be a normal feature. The peculiar condition 

 found in thi< region in specimen No. 7523, University of Michigan, is described below, 

 but is not yet understood. 



The articulation with the maxillary starts on the alveolar edge, just posterior to 

 the twenty-third tooth. The surface of the premaxillary is devoid of rough sculpture, 

 unless it be at the extreme posterior end, where it approaches the nasal prominence just 

 anterior to the external nan-. 



The maxillary has the usual position and relationships. It forms the lower border 

 and the anterior border of the antorbital vacuity and the anterior part of the upper 

 border of the same opening. The portion below the vacuity is smooth and the alveolar 

 edge is convex downward. There are 21 tooth-sockets in the maxillary, which are 

 rounded in the anterior portion, but by the eighth or tenth from the anterior end become 

 decidedly oval in outline. The upper portion of the maxillary is more rugose. The 

 position of the suture between it and the nasals is indicated by the sudden increase in 

 the coarsenesi of the rugosities, as well as the change in the course of the bone-fibers. 



