PROFESSOR OWEN ON THE GENUS PALAPTERYX. 361 



of the Dinornis casuarinm, but which, from the minor degree of descent of the basioc- 

 cipital, the position of the precondyloid foramina (p), the size and form of the single tym- 

 panic articular cavities of the mastoid, and the large development of the olfactory cham- 

 bers, is referable to Palapteryx, one postfrontal, the left, is fortunately entire, and yields 

 another mark of difference from the cranial structure of Dinornis proper, viz. the non- 

 union of the postfrontal (12) with the mastoid (s). The postfrontal is a large triangular 

 process, depressed, standing outwards, with a slight curve downwards and backwards, 

 having the upper surface divided into a frontal and temporal facet, and the under 

 surface deeply excavated at the base of the process (fig. 5, 12). 



In a more mutilated cranium of apparently the same species of Palapteryx (PI. LV. 

 fig. 6), the form and proportions of the cerebral lobes and cerebellum are well shown, 

 by the projection of the inner table of the cranium into the cellular diploe. 



Skull 0/ Palapteryx geranoides (?). 



The second almost entire cranium in Mr. Mantell's rich and instructive collection 

 (PI. LIV.) agrees with those assigned to Palapteryx in all the characters by which they 

 differ from the cranium assumed to belong to Dinornis (PI. LII.) ; viz in the minor 

 descent of the basioccipital (1, 1", fig. 4), the square platform of the basisphenoid (5, fig. 3), 

 the higher position of the precondyloid holes {p, fig. 4) and their separation from the 

 carotid holes (c), the minor development of the paroccipitals (4), the major development 

 of the mastoids (s) and olfactory chambers (is, fig. 3), and especially in the large and 

 single oblong depression (y, fig. 3) beneath the mastoid for the single superior condyle 

 of the tympanic; The occipital condyle (figs. 2 & 4, 1') forms the lower half of a 

 hemisphere, but is not notched above and reniform as in the Dodo. The occipital 

 foramen (0) is subcircular, broadest transversely. The descending basioccipital is 

 impressed by a pit, divided by a median ridge, and bounded below by the straight 

 posterior border of the basisphenoidal platform, the ends or angles of which are smooth 

 round tuberosities (1", figs. 3 & 4). The precondyloid foramina {p) are proportionally 

 larger than in Dinornis, and on the same transverse line as the condyle. The descent 

 of the basioccipital is somewhat less in Didus, but it also expands into two thick obtuse 

 processes from which muscles pass to the inwardly bent angles of the lower jaw. 

 Internal to these processes (3, 3), in Didus, are two short tubercles. The paroccipital 

 processes (4) are semicircular plates, compressed from before backwards, divided by a 

 notch from the basioccipital tubercles, in which notch is situated the entry to the 

 carotid canal (c). The supraoccipital region is less bent forwards than in Dinornis, and 

 is divided into two by a marked median vertical ridge : the subdivision of the halves is 

 very slightly indicated by the bending down of the supraoccijiital ridge midway between 

 the median ridge and the paroccipitals (4,4), but the tuberosities are much less strongly 

 marked than in Dinornis. 



VOL. III. — PART V. 3d 



