Se 
80 
one-third ; in the smallest metatarsal (m 4)! it is a little more than one-half. Again, the 
breadth of the distal end of the smallest metatarsal is nearly one-half the length of the 
bone; in m3 it is just one-third; in m1 it is two-sevenths. The difference is well 
marked in the proportions of the breadth or lateral diameter of the shaft, as compared 
with the thickness or antero-posterior diameter, but is less between m 1 and m3 than 
between either of these and m4 or m 9. In regard to these smallest-sized metatarsals, 
they both present differences of configuration when compared with the larger metatarsals, 
besides those indicated by the admeasurements, which assist in establishing a distinction 
of species : the distal end of the bone is more suddenly expanded than in the larger speci- 
mens ; the proximal posterior prominence of the middle division of the metatarsal more 
rapidly subsides as it descends ; there is no longitudinal channel continued downwards 
from the hole on the inside of this prominence, such channel being as well marked in the 
larger metatarsals as the outer one: the shallow concavity on the outside of the promi- 
nence is relatively broader in the smaller metatarsals. ‘The inner concavity of the proximal 
articular surface is relatively deeper in m4. The median longitudinal concavity, below 
the rough depression at the anterior part of the proximal end of the bone, is hardly dis- 
cernible in m4, but is well marked in m 1 and m3. Finally, the small metatarsal, which 
is but half the length of m3, and but one-third the length of m 1, has all the characters 
of the compound tarso-metatarsal in a fully mature bird : there is no trace of the original 
separation of the proximal epiphysis ; and, with respect to that of the three primitive 
constituents of the shaft of the bone, it is as obscurely indicated as in other old tridactyle 
birds, by the two small holes at the back and upper part of the bone. I infer, there- 
fore, from the smallest metatarsals, m 4 and m5, which have the same characters and 
nearly the same size, the former existence of a distinct species of three-toed Struthious 
bird, differing from the larger species of Dinornis in its relatively shorter and broader me- 
tatarsus. In this character the present species of Dinornis closely resembled the extinct 
Dodo (Didus ineptus, Linn.) of the Isles of France and Rodriguez ; and as it could not 
have been greatly superior in size, I propose therefore to designate it Dinornis didiformis. 
Like the larger species of Dinornis, there is not the slightest trace of the articulation 
of a fourth or posterior toe in the metatarsal of the Dinornis didiformis ; the generic di- 
stinction from Didus and Apteryz being thus distinctly indicated in all the tarso-metatarsal 
bones of the present collection. 
If the different proportions and configurations of the smallest tarso-metatarsal bones 
justify the conclusion that they belonged to a particular species of Dinornis, by parity of 
reasoning the same inference must be drawn in regard to the intermediate-sized tarsu- 
metatarsal, m3, which is far from repeating the proportions of the largest bone, m 1, as 
the table of dimensions already referred to demonstrates: m3 is in fact a more robust 
bone, in proportion to its length ; the anterior longitudinal concavity, commencing below 
the rough depression, is deeper ; the channel leading to the cleft between the condyles 
| Pl, XXVII. fig, 3—6. 

