6 
Palapteryz it is single, as in Apteryx. In Didus the tympanic bone 
is subquadrate with the four angles produced, and the upper and 
hinder one bifurcate, forming the bifid condyle for the mastoid arti- 
culation: in Dinornis the mastoid condyle is also double, with a 
linear strip of bone between ; and behind this the pneumatic foramen, 
where also similar foramina are situated in Didus: in this extinct 
bird, the orbital process, forming the anterior angle, is compressed 
and truncate: the outer surface of the bone is smooth and convex 
vertically ; the inner surface is traversed by a sharp concave ridge 
extending from the inner division of the upper condyle to the ante- 
rior part of the inner and lower angle: the anterior division of the 
inner surface is concave, the posterior one is concave vertically, con- 
vex transversely. The antero-posterior extent of the condyle for 
the lower jaw is little, but greatest at its outer part, where it rests 
upon the shallow reniform outer division of the concave articular 
part of the lower jaw: the inner, more ridge-like part of the condyle 
sinks into a deeper transversely extended depression of the same 
articular concavity. The tympanic of the Dinornis chiefly differs in 
the great extension, upwards and backwards, of the broad and un- 
divided inferior condyle: there is also an articular surface, on its 
outer side, for the mastoid process (not present in Ofis) and another 
small one on the inner side for the pterygoid; besides the lower and 
outer cup for the end of the slender zygoma (squamosal). 
The inner angle of the expanded articular end of the lower jaw 
of Dinornis ends by a short obtuse process. In Otis and Didus it 
forms a strong trihedral process, the anterior and posterior facets 
meeting a transverse ridge below, which is continued into a com- 
pressed plate forming the posterior angle of the jaw. The posterior 
surface is smooth and slightly concave, semioval in Dinornis, deeper 
and subtriangular in Didus. r 
The outer part of the articular end of the mandible is smooth and 
convex in Dinornis: in Didus a masseteric ridge is continued down- 
wards and forwards from the outer overhanging border of the arti- 
cular cavity to the back and lower angle of the dentary piece, de- 
fining, with the posterior border of the dentary, a concave, slightly 
pitted surface. The surangular in Dinornis hasa short and low thick 
coronoid ridge, external to which there is a rough oval surface. In 
Didus the surangular developes a very small coronoid process, and 
its fore-part is deeply notched: a deeper and more angular notch 
divides the surangular from the angular piece. This notch receives 
the lower fork of the dentary on the outside, and the end of the 
splenial at the inner side. These notches do not exist in Dinornis : 
the surangular, angular and articular pieces have coalesced together 
in both the extinct birds. Where they join the posterior forks of 
the dentary piece, a long narrow vacuity is left, which in Dinornis is 
almost divided by a broad bar of bone extending upwards from the 
angular, but which does not quite touch the surangular. In Didus 
the upper fork of the dentary joins the upper and fore part of the 
surangular; the notch between the hinder forks of the dentary bounds 
anteriorly the narrow elliptic vacuity, 15 millimeters long by 3 milli- 
