CLASSIFICATION, AND PHTLOGENT OF THE DINORNITHID^. 411 



Temporal fossa nearly vertical ; distance between temporal ridges about equal to 



width of cranium at temporal fossse. 

 Zygomatic process narrow and outstanding ; no squamosal prominence. 

 Width of orbit considerably less than width of cranium at paroccipital processes, 



and about one and a half times length of basis cranii ; interorbital septum 



present ; supraorbital ledge continued into cranial crest and produced behind into 



a broad, nearly vertical, postorbital process. 

 Orbital process of lacrymal united with cranial crest, only its posterior end projecting 



as a short, backwardly-directed process ; descending process notched for lacrymal 



duct and sending off, ventrad of the latter, a short upwardly-directed process from 



its lateral margin, which partly converts the notch into a foramen. 

 Antorbital well ossified and ankylosed laterad with descending process of lacrymal ; 



a deep Harderian fossa. 

 No descending process to nasal ; the specimen examined does not show whether the 



mesethmoid is covered by the nasals, but it appears to be so '. 

 Premaxilla strong ; body high and strongly ridged, with a distinct prenarial septum ; 



narrow palatine processes ; width of body about half length of basis cranii. 

 Maxilla reaches nearly as far forward as prenarial septum ; maxillo-palatine an 



elongated cone with the apex directed forwards, and contains a spacious antrum 



opening behind by a wide aperture. 

 Vomer nearly three times length of basis cranii ; flattened and obscurely grooved in 



front, deeply forked behind ; ankylosed to palatines and pterygoids. 

 Palatine a short oblique plate, nearly one and a half times length of basis cranii, 



articulating anteriorly with the maxilla and ankylosed posteriorly with the vomer 



and pterygoid. 

 Mandible weak ; symphysis narrow, pointed, and keeled below. 



Aptertx. 



Occipital plane inclined at an angle of 45° to the basis cranii ; occipital condyle 



pedunculated ; occipital crest variable. 

 Length of cranial roof less than three times that of basis cranii. 

 Mamillar processes very large and prominent. 



Width at paroccipital processes about double length of basis cranii. 

 Width at squamosals nearly double length of basis cranii. 

 Height of cranium less than one and a half times length of basis cranii. 

 Temporal fossa very wide and nearly vertical; distance between temporal ridges 



equal to width of cranium at temporal fossae. 



' See, however, 25, p. 428. 



