514 PROFESSOR OWEN ON THE 
vertebra. And in the instructive example of the three partially anchylosed vertebree of 
a young Pezophaps (pl. 16. fig. 60, N.) the third vertebra shows no hypapophysis’. In 
this specimen anchylosis is seen to have begun at the neural arch and spine, chiefly be- 
tween the first and second vertebre, and co-ossification of the centrums is more advanced 
between the first and second than between the second and third of these vertebre. 
The inference that these anchylosed vertebre included the penultimate, antepenulti- 
mate, and the next dorsal vertebra in advance, and that only one free dorsal vertebra 
intervened between the coalesced mass and the sacrum, was confirmed by the specimens 
of Pezophaps (N., p. 332), as it has been by additional vertebre of Didus; and the 
correspondence of both the extinct Mascarene species with the Columbide in this 
vertebral character must now be held to be well established. 
One would be glad to receive the evidence of the vertebral formula which the entire 
skeleton of one and the same individual of Didus or Pezophaps would afford; but 
the discovery of such with the bones in requisite contiguity is hardly to be hoped for. 
The concurrence, therefore, of Messrs. A. & E. Newton, as to the number of moveable 
thoracic or dorsal ribs*, with the estimate similarly formed from comparison of detached 
vertebree of Didus*, is welcome. 
To both the Mauritian and Rodriguez extinct Ground-Doves may be referred eight 
pairs of dorsal ribs. For the similarity of size and proportions of some of these ribs, 
and of the confluent epipleural appendage, figures 5 & 7, pl. 16 (O.), may be compared 
with figures 63 & 64, pl. 16 (N.). 
The first material discrepancy between Didus and Pezophaps, or between the descrip- 
tions of their respective osteologies here quoted, is in the number of sternal ribs. 
To Messrs. Newton there appear to be only four pairs in Pezophaps, the last articu- 
lating with the sixth dorsal rib‘. It is to be regretted that the mutilated lateral border 
of the best-preserved sternum of Pezophaps, one of six received by the Messrs. Newton, 
does not allow a certain conclusion to be arrived at as to the number of articular surfaces 
on the costal border. 
Messrs. Newton do not entertain so much doubt on this point as I do; they write :— 
“A more remarkable difference is presented by the costal border in this” [their best- 
preserved] ‘‘ specimen, which shows articular surfaces for four sternal ribs only, instead 
of five, which is the normal number in Dzdus ; and, so far as can be determined from the 
broken state of the remaining specimens, there is nothing to induce the belief that they 
possessed more than four such surfaces”®. 
If any one will compare fig. 2, pl. 18, O., with fig. 74, pl. 18, N., he may be allowed 
to doubt whether the fracture following the fourth articular surface on the costal 
border of the least-mutilated sternum of Pezophaps may not have removed a fifth 
‘ Tn other respects the last of the three anchylosed dorsal vertebrae in Pezophaps does “ bear a great general 
resemblance to the same bone in Didus.” 
2 N., p. 332. 3 0., p. 53. 4 N., p. 334. °N., p. 338. 
