420 PEOF. T. JEFFERY PAEKER ON THE CRANIAL OSTEOLOGY, 



Width of body of premaxilla nearly equal to its length, and about three fourths of 



the length of the basis cranii. 

 Prenarial septum distinct. 



Maxillo-jugal rather slender, compressed posteriorly, and strongly curved. 

 Orbital process of quadrate compressed and bluntly pointed ; a single pneumatic 



foramen of variable size on the mesial surface of the otic process. 

 Mandible strong, V-shaped, moderately deflected; posterior angular process of 



moderate size. 



Genus Mesopteryx. 



Occipital plane vertical or inclined backwards ; occipital crest usually distinct ; 



supraoccipital fossae present. 

 Occipital condyle often projects beyond paroccipital processes. 

 Paroccipital process pointed ; width of cranium at paroccipital processes about one 



and a half times length of basis cranii. 

 Width at squamosal prominences double length of basis cranii. 

 Mamillar tuberosities small ; posterior border of basitemporal platform nearly 



straight. 

 Margin of tympanic cavity right-angled (evenly curved in species a). 

 Temporal fossa small ; distance between temporal ridges about equal to width of 



cranium at temporal fossae ; width of temporal fossa about one half length of basis 



cranii. 

 Temporal and lambdoidal ridges never confluent. 

 Posterior temporal fossa narrow ; inferior temporal ridge moderate. 

 Margin of orbit evenly curved or slightly sinuous (right-angled in species y) ; post- 

 orbital process evenly curved. 

 Trigeminal foramen usually double (single in species /3), consisting of apertures 



placed one above the other and separated by a narrow horizontal or oblique bar. 

 Distance between optic foramina about one third length of basis cranii. 

 Antorbital very thin ; supraorbital fenestra rather small ; postchoanal ridge very 



thin or barely discernible. 

 Rostrum dilated but not flattened towards its posterior end, usually much compressed 



and carinate in its intermediate portion, and slightly dilated between and in front 



of the triangular processes. 

 Body of premaxilla narrow and pointed ; its width nearly equal to its length and 



about three fourths length of basis cranii ; a distinct prenarial septum. 

 Maxillo-jugal arch slender and gently curved. 

 Orbital process of quadrate compressed and bluntly pointed ; a single pneumatic 



foramen of variable size on mesial surface of otic process. 



