280 
explicable, as Dr, Haast suggests, as a sexual character ; the specimen noted as yielding 
* the smallest size” is, as Dr. Haast remarks, of a bird not quite full-grown. 
The difference in the proportions of the leg-bones between Dinornis rheides and 
D. casuarinus is greater in respect of robustness than of length, yet not in such a degree 
as to make the decision come to as to their specific distinction one lightly arrived at, 
or without well weighing many particulars. In the memoirs defining these species I 
troubled the Society mainly with the results, omitting particulars of the processes 
leading thereto. But I could not have ventured to anticipate that a certain comparative 
slenderness of the hind limbs would have been associated with a beak shorter and 
weaker in the degree demonstrated by the skull of D. caswarinus above described. 
Skull of Dinornis gravis, Ow. (Plate LXXXI.) 
Many characteristic parts of the skeleton of the same individual bird were obtained 
by Witttam Fenwick, Esq., at the Kahamin River, Middle Island, New Zealand, and 
were presented by that gentleman to Miss A, Burdett Coutts. 
Dinornis gravis was of about the same stature as D. rheides, and as the characteristics 
of cranial structure will be better appreciated in both birds by contrast and comparison, 
I give a description of the skull of the new species in the present Memoir. 
Dinornis gravis presents the shortest mandible in proportion to the breadth of the 
skull that I have yet observed in that genus. The breadth of the occiput being equal to 
that of Dinornis crassus, the occipital condyle and foramen magnum are less, especially 
the latter (comp, fig. 4, Pl. LX XXL, with fig. 3, Pl LXXVI.). The superoccipital tract 
slopes more forward, is more continuous with the general longitudinal upper convexity of 
the cranium. ‘The basisphenoidal platform is longer in proportion to its breadth; it 
shows a large central orifice of a canal extending upward and backward. ‘The alisphe- 
noidal tuberosity (fig. 4, 6) is more prominent and divided from the pterapophysis by a 
deeper and narrower fissure. The foramen ovale is divided by a better-marked bar into an 
upper smaller and lower larger division. The paroccipital bends down from the mastoid 
more abruptly, at a right angle to the connecting ridge, in order to form the back part of 
the tympanic fossa. The temporal depression is relatively smaller, especially in antero- 
posterior diameter; an extent of 1 inch 9 lines intervenes at the upper part of the 
cranium between these fosss (fig. 3). The postorbital process is triangular, more rapidly 
decreasing in breadth as it descends, and its outer plane is directed more backward, less 
outward, than usual. The presphenoidal rostrum, 2 inches 8 lines in length, is com- 
pressed at its middle part below, expanded and convex before and behind this ridge, 
pointed anteriorly and confluent throughout its upper extent with the prefrontals and 
orbito-sphenoids. ‘The “shelf” (Pl. LXXX1., fig. 4,9”) extends further outward than in 
Dinornis crassus or D. rheides. A broad vertical lamina, continued from the lachrymal 
and the olfactory girdle, descends external to the posterior olfactory orifice almost to 
the level of the presphenoid, forming the anterior wall of the orbit, ‘The fronto-nasal 
