CLASSIFICATION, AND PHTLOGENT OF THE DINORNITHID^. 413 



Zygomatic process short, pointed, and nearly parallel to median plane ; auditory 

 region of skull produced into a strong squamosal prominence. 



Width of orbit about half width of cranium at paroccipital processes, and almost 

 invariably less than length of basis crauii ; interorbital septum absent or greatly 

 reduced ; a broad supraorbital ledge, produced behind into a strong, broad, post- 

 orbital process. 



Lacrymal ankylosed with frontal, forming a preorbital process ; no orbital process ; 

 a descending process ankylosed with outer border of antorbital and notched or 

 perforated for lacrymal duct. 



Mesethmoid produced into paired horizontal triangular processes. 



Antorbital well ossified ; ankylosed to descending process of lacrymal ; perforated 

 dorsally by a supraorbital fenestra of variable size. 



Nasal either has a slender maxillary process, or there is a distinct maxillo-nasal bone ; 

 meets its fellow of the opposite side in the middle line above the ethmoid, so that 

 the latter does not appear on the dorsal surface ; premaxillary groove on upper 

 surface of nasals extends backwards to or beyond naso-frontal suture. 



Premaxilla strong ; body more or less elevated, and with a distinct prenarial septum ; 

 palatine processes broad and produced into more or less definite vomerine processes ; 

 width of body always more than half and sometimes one and a half times length of 

 basis cranii. 



Maxilla short and narrow ; maxillo-palatine a short, flat plate, produced dorsad either 

 into an irregular shell of bone containing a large antrum, or into a thick, oblique 

 plate, containing no, or but little, trace of the antrum. 



Vomer less than one and a half times length of basis cranii ; consists of thin paired 

 plates meeting each other ventrad in an acute dihedral angle, and either quite 

 free or partially ankylosed with one another in front ; firmly ankylosed behind, in 

 fully adult specimens, with palatines and pterygoids. 



Palatine a thin twisted plate, about one and a fifth times length of basis cranii ; 

 pedate posterior end produced into short mesial vomerine process ; articulates at 

 anterior end with maxilla, and posteriorly with vomer and pterygoid, with which, 

 in fully adult specimens, it becomes ankylosed. 



Mandible very strong ; symphysis short, more or less flattened and ridged below ; 

 distal end more or less deflected downwards. 



7. The Classification of the DiNOENiTHiD.a;. 



At an early period of his investigations — in 1846 — Owen was led to the conclusion that 

 the differences between certain of the Moas were of more than specific value, and 

 instituted the genus Palapteryx for the reception of species (ingens and dromioides) in 

 which the hallux was present. Further investigations, however, convinced him that 

 the retention of a purely vestigial structure was not, even if constant, of sufficient 



VOL. xrii. — PART XI. No. 6. — October, 1895. 3 N 



