Prof. R. Owen on the Solitaire. 87 
each other both in the shape and markings of their casques, 
and also in the distribution of the colours of the plumage. 
They can be distinguished as follows :— 
Key to the Species. 
A. Median pair of rectrices black, with’ green reflec- 
tions. 
a’. Lateral rectrices pure white. 
a'', Size large ; black mark on casque never 
reaching the maxilla’ iP. viscid S005 0 1. A. coronatus. 
6". Size small; black mark on casque extend- 
ing onto the maxilla, .. 6. .igacsgeee 2. A. converus. 
6'. Lateral rectrices with their apical third white. 
a", Size large ; black mark on casque reach- 
ing onto the maxilla:............... 3. A. malabaricus. 
b". Size small; black mark on casque not 
reaching; the maxilla... 6s en+ es een 4. A. fraterculus. 

XII-—On the Solitaire (Didus solitarius, @m.; Pezophaps soli- 
taria, Strkl.). By Prof. R. Owen, C.B., F.R.S., &e. 
(Plates VIL & VIII.] 
Bones of this extinct bird collected in the island of Rodriguez 
during the “ Transit-of-Venus”’ expedition, and now in the 
British Museum, have supplied materials for the articulation 
of the entire skeleton, and the subjects of the following notes. 
In the skeleton of both male (PI. VII. fig. 1) and female 
Pezophaps, the number of cervical vertebre is 12, that of the 
dorsal 6, a 7th free-rib-bearing vertebra being made “ sacral”’ 
by ankylosis with the rest of that coalesced group of bones. 
So much of the vertebral formula thus accords with that of 
Didunculus *. As in that dove, also, the three middle dorsal 
vertebrée (third, fourth, and fifth) have coalesced, and their 
square truncate spines form a strong bony crest. Four pairs 
ot ribs are connected, by ossified hemapophyses, with the 
sternum; and this bone deviates mainly from the columba- 
ceous type by the minor development of the keel, in relation 
to the atrophy of the chief muscles of flight. 
Sixteen coalesced vertebree constitute the sacrum of Pezo- 
phaps as of Didus; and seven free vertebre beyond the pelvis 
support the tail-feathers. Thus the vertebral formula of 
Pezophaps is: 

C. 12, D. 6, 8. 16, Cd. 7,=41. 
* See the figure of the skeleton of the didiform species of the Samoan 
Islesin my ‘Memoir on the Dodo,’ 4to, 1866, pl. ii. fig. 2. 
