THE UPPER TRIASSIC OF WESTERN TEXAS. 69 



9. Septomaxillary present. 



10. Premaxillary and maxillary teeth, 41 , round and oval, with serrate edges. 



11. Palatine with inner edge elevated into a ridge. The palatine vacuity between the palatine, pterygoid, and 



the anterior half of the transverse. 



12. Transverse meets the external edge of the pterygoid. No external process of the pterygoid. 



13. Vomers do not appear behind the internal nares. 



14. Parasphenoid process long, eovered anteriorly by the pterygoids. 



15. Interpterygoid vacuity short, narrow. 

 Ph ytosaurus (Machceroprosopiis) : 



1. Post-temporal arcade depressed; not visible from above. 



2. Anterior end of the antorbital vacuity anterior to the external nares; elongate oval. 



3. Length of the prenarial portion of the skull is to the postnarial as 3 : 2. 



4. Pos1>temporal fenestra large. 



5. No posterior bar on the parietal; the postorbital takes the place of the parietal on the posterior edge of 



the skull. 



6. External nares without elevated rim, septum at the level of the top. 



7. Squamosal region greatly extended posteriorly, with a strong hook. 



8. Orbits look outward more than upward; slightly forward. 



9. Septomaxillaries large, united in front and form a prominence, "if correctly determined" (Mehl). 



10. Premaxillary and maxillary teeth 36-38; both rounded and oval in section. 



11. Palatal surface of the skull unknown. 

 Mystriosuchus: 



1. Post-temporal arcade depressed. 



2. Anterior end of antorbital opening anterior to the nares; nares over the middle of the opening. 



3. Length of the prenarial portion of the skull is to the postnarial as 5 : 2. 



4. Post-temporal fenestra small. 



5. Posterior bar of the parietal depressed, lying on the opisthotic, long. 



6. External nares with elevated rim, septum at upper level; internal nares directly under the external nares. 



7. Squamosal region extended posteriorly. 



8. Orbits look outward more than upward; upward in M. pleiningcri. 



9. Septomaxillary present. 



10. Premaxillary and maxillary teeth 47-50, both rounded and oval in section. 



11. Inner edge of palatine elevated; palatine vacuity opposite the middle of the transverse. 



12. Transverse underlies the external process of the pterygoid. 



13. Vomers do not extend posterior to the internal nares, or very little. 



14. Parasphenoid process fairly long, anterior end covered. 



15. Interpterygoid vacuity small. 

 Promystriosuch us: 



1. Post-temporal arcade at the level of the skull. 



2. Anterior end of the antorbital opening opposite middle of external nares; elongate oval. 



3. Length of prenarial portion of the skull is to the postnarial portion as 3 : 2. 



4. Post-temporal foramen small. 



5. Posterior bar of the parietal long. 



6. Rim of external nares elevated, septum low; position of the internal nares posterior to external. 



7. Squamosal region not greatly extended posteriorly. 



8. Orbits look upward, perhaps in part due to crushing. 



9. Septomaxillary (?). 



10. Premaxillary and maxillary teeth 47; both oval and rounded in section. 



11. Inner edge of palatine raised anil rugose. Palatine vacuity small, near middle of transverse. 



12. Transverse underlies the outer process of the pterygoid. 



13. Vomers (?). 



14. Parasphenoid process long; anterior end probably covered by the pterygoids. 



15. Interpterygoid vacuity long. 

 Leptosuchus: 



1. PosHemporal arcade depressed. 



2. Antorbital opening with the anterior end even with the anterior end of the nares; oval in outline. 



3. Length of the prenarial portion of the skull is to postnarial portion as 3 : 2. 



4. Post-temporal fenestra small. 



5. Posterior bar of the parietal long, lying on the opisthotic. 



6. External nares without rim, septum at level of the skull. Internal nares directly below the external. 



7. Squamosal extended posteriorly with a strong descending process; overhanging the bones below. 



8. Septomaxillary present. 



9. Orbits look upward and outward. 



10. Premaxillary and maxillary teeth 44; both rounded and oval in section. 



11. Inner edge of palatine strong, a low ridge; palatine foramen small, opposite middle of transverse. 



12. Transverse underlies the pterygoid. 



13. Vomers do not appear on the palatal surface. 



14. Parasphenoid process long, covered anteriorly by the pterygoids. 



15. Interpterygoid space short and narrow. 



