CLASSIFICATION, AND PHTLOGBNT OF THE DINORNITHID^. 



425 



Rhea 



than any other tjenus to Brommus and Casuarius '. On the other hand, the relative 

 size of the orbit is greatest in Anomalopteryx, and the presphenoid fossa or vestige of 

 the interorbital septum is most marked in that genus and in Binornis: I am disposed, 

 therefore, to derive Mesopteryx and Anomalopteryx from a common ancestor. 



Pachyornis appears undoubtedly to spring from the Mesopteryx-stock : these two 

 genera are more nearly allied than any other two, Pachyornis being the more differen- 

 tiated in virtue of its greater bulk, broader skull, larger temporal fossEe, more widely 

 separated optic foramina, and stronger beak. 



JEnieus is derived by Hutton from Mesopteryx, a view which I am strongly inclined 

 to adopt. The cranium of Emeus undoubtedly comes nearest to that of Mesopteryx, 



Dinornis 



Casuarius 



Shruthio 



M 



Oron 



Emeus 



ftPachyornis 



Me^optcPvx Anomalo 

 ^ ' . pteryxJU 



Apteryx 



Fig, 1. — Phylogenetic diagram sho\ving the mutual relations of the Ratitse. 



the differences between the two skulls depending mainly on the stronger and coarser 

 character of the whole skull, the broader beak, and the stronger mandible of Emeus. I 

 think, therefore, that the latter genus should be considered as springing from the 

 Mesopteryx-stock—Tiot, of course, from Mesopteryx itself, but from an older member of 

 the line of descent which culminated in that genus. 



Binornis agrees with but goes beyond Pachyornis in its widely, separated optic 

 ' The striking resemblance of the dried head of Mesopteryx casuarina (Didomis didinus, Owen) to that of 

 an Emu is noticed by Owen (23). 



