214 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 20, 



original degree of concavity : the margins were, however, evidently 

 more developed than in the Swan. 



The general proportions of the fossil tibia from the Paris eocene, 

 fig. 1, are most like those of the Binornis easuarinus, fig. 2 : the size 

 is nearly the same. The differences at the distal end are seen in the 

 more median position of the supratendinal bridge, e, in the Gastornis; 

 it is close to the inner side in the Binornis ; in the absence of the 

 depression below the outlet in the Binornis ; in the greater posterior 

 breadth of the trochlea in Gastornis ; and in a greater antero-poste- 

 rior diameter of the inner side of the shaft. The shallow groove and 

 low tuberosity external to the canal are present in both these extinct 

 birds. 



From the tibia of the Solitaire (^Pesophaps), that of the Gastornis 

 differs in the more median position of the bridge, and in the depres- 

 sion below the bridge : in other respects it makes'a close approxima- 

 tion to that extinct bird. 



The Aptornis further differs from the Gastornis in the wider inter- 

 condyloid space, and in the narrower and (probably) more prominent 

 inner condyle ; but the mutilated state of that part in the Parisian 

 fossil prevents a decided opinion on this point. 



The Notornis resembles the Gastornis in the median position of 

 the bridge, but differs in the absence of the depression below it, in 

 the aspect and shape of the lower outlet, in the wider intercondyloid 

 space and narrower inner condyle, and in the well-developed outer 

 boundary of the canal leading to the bridge. 



Conclusion. — Having made the foregoing observations and com- 

 parisons of the tibiae of recent and fossil birds with that of the Gast- 

 ornis, as much as possible independently of any preconception or bias 

 from previous opinions published as to the nature and affinities of that 

 bird, I propose to review those opinions, commencing with the remarks 

 of M. le Prof. Hebert, who has given a very accurate description of1;he 

 fossil in question. After rightly pointing out the gradual increase of 

 the transverse over the antero-posterior diameter of the bone as the 

 lower fourth of the shaft api)roaches the condyles, he remarks : — 

 " Get aplatissement du tibia est tres remarquable et constitue un bon 

 caractere distinctif *." It offers a marked difference as compared 

 with the tibia of the large species of Crane {Ciconia), Stork (Grus), 

 Bustard (Otis), and most Waders, and also from the Gallince and 

 the Natatores, especially in the development of the ridge or angle 

 between the fore and outer surfaces of the bone leading to the outer 

 condyle. The Eagle shows something like this, which is due to the 

 anchylosed lower point of the fibula, which forms the corresponding 

 ridge ; the lower third of the til^ia in all tlie great Aquiline birds is 

 proportionally more compressed from before backwards ; but the inner 

 side is by no means so thick antero-posteriorly. The correspondence, 

 however, between the Gastornis and the Binornis casuarinus in the 

 general form and proportions of the lower end of the tibia is very 

 * Compte Rendu de TAcademie des Sciences, Mars 12, 1855, p. 579. 



