82 
individual of the same species of Dinornis as that to which the great tarso-metatarsal 
bone m1 belonged, virtually assumes that the relations which modify the progress of 
ossification were different in the Dinornis from what they are in the Ostrich, and that a 
bird which, from the non-extension of the air-cells into the femur, was as poorly en- 
dowed with powers of flight as the Apteryx, and consequently possessed of as compara- 
tively low circulating and respiratory energies, must at the same time have enjoyed as 
rapid an ossification of the skeleton as the Swailow; postulates which, being contrary 
to known physiological correlations, are inadmissible. 
Since, therefore, the tarso-metatarsal m3 combines with the characters of a fully de- 
veloped bone, a marked difference of size, different proportions, and some minor modi- 
fications of form, as compared with the large bone m 1, it must indicate a second species 
of Dinornis, which, as it attained, as will be presently shown, the average height of the 
Ostrich (Struthio camelus), I shall call Dinornis struthoides.. 
That the Dinornis struthoides is, in fact, a good and true species, is put beyond all 
cavil or doubt by the existence of a tarso-metatarsal bone (m2)' which is longer than 
m3, but agrees in the proportions and form of its shaft with m1, and manifests the 
same characters of immaturity which have been already noticed in the corresponding 
bone of the young Ostrich, Here, therefore, we actually have, what m3 might have 
been mistaken for, a bone belonging to a young individual of the gigantic species 
(Dinornis giganteus). 
The condition of this young bone demonstrates, what could not indeed be reasonably 
doubted, that a more tardy ossification coexists in the Dinornis, as in other Struthionide, 
with the absence of the powers of flight; and as such a condition in the present bone 
establishes the maturity of the tarso-metatarsal bone m 3, which it exceeds in length, 
it proves, @ fortiori, that the smallest tarso-metatarsal, with all the characters of mature 
age, could not have belonged to a young individual of either of the two larger species. 
Or, in other words, if the young of the Dinornis giganteus, when the shaft of its tarso- 
metatarsal bone is eleven inches long, manifests evident marks of immaturity, these 
characters ought to have been more strongly marked in the shorter tarso-metatarsals 
m3? and m 5%, if they had really belonged to young individuals of the largest species. 
The marks of immaturity in the shaft of the tarso-metatarsal of the young Dinornis gi- 
ganteus, m 2, are the gradual deepening and widening of the anterior median channel of 
the shaft as it approaches the proximal end of the bone, until it divides into the fissures 
separating the proximal ends of the three constituent metatarsals, which extremities in 
the specimen are broken off immediately above the point where they begin to coalesce. 
In a specimen of the tarso-metatarsal bone, m6, of the Dinornis didiformis, in which the 
proximal end is broken off a few lines above the anterior rough depression which indi- 
cates the primitive dividing groove, the constituent metatarsals are faintly indicated by 
' Pl. XXVIIL. fig. 3. * Tb. fig, 5. * Ib. figs, 6 & 7. 
