242 PROFESSOR OWEN ON THE GENUS DINORNIS. 



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 m 3 it is just one-third ; in ?« 1 it is two-sevenths. The difference is well 

 ni;u'ked 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 m 3 than 

 between either of these and m 4 or m 5. In regard to these smallest-sized metatarsals, 

 the}' 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 m 4, but is well marked in m 1 and m 3. Finally, the small metatarsal, which 

 is but half the length of m 3, 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 m 5, 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 oiDinornis in its relatively shorter and broader me- 

 tatarsus. In this character the present species of Dhiornis 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 shghtest trace of the articulation 

 of a fourth or posterior toe in the metatarsal of the Blnornis didiformis ; the generic di- 

 stinction from Didus and Apteryx 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 Dmorm's, by parity of 

 reasoning the same inference must be drawn in regard to the intermediate-sized tarso- 

 metatarsal, m 3, which is far fi'om repeating the proportions of the largest bone, ?w 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 



' PI. XXVII. fig. 3—6. 



