36 
intervened between the coalesced mass and the sacrum, was confirmed by the specimens 
of Pezophaps (N., p- 332), as it has been by additional yertobie 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 has yet to be made. The 
concurrence, therefore, of Messrs. A. & E. Newton, as to the number of movable thoracic 
or dorsal ribs’, with the estimate similarly formed by myself from comparison of detached 
vertebrae 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 and second are wanting in the subject of 
PL I. 
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*: four only are preserved in the articulated skeleton of 
the Dodo (Pl. I.). 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 Didws ; 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 
narrow ridge like that (fig. 2, pl. 18, O., ¢5) to which the fifth sternal rib articulates 
in Didus. Admitting, however, that ‘too much importance must not be placed on this 
character”®, and cognizant of instances, like that cited by Messrs. Newton, of jive 
articular surfaces on one side, and four on the other, yet I am unwilling to suppose 
that the last (in Didus, “sixth”) sternal rib, which terminates below in a point and 
joins the antecedent sternal rib before attaining the sternum, had not its homologue in 
Pezophaps. I quite concur, however, with the observant and conscientious authors of 
'N,, p. 332, * 0., p, 53. 7 N., p. 334. ‘ N., p. 338, ‘N., p. B38. 
