Zoological Society. 55 



the tympanic cavity is cellular in Didus. The eustachian outlets 

 open, in both Dinornis and Otis, above a transverse ridge terminating 

 the basisphenoid anteriorly : this ridge is not present in Apteryx or 

 Palapteryx. The Palapteryx also differs from Dinornis in the higher 

 position of the precondyloitl holes and their greater separation from 

 the carotid holes, in the minor development of the paroccipitals, the 

 major development of the mastoids, and by the large and single 

 oblong depression, beneath the mastoid, for the single superior con- 

 dyle of the tympanic bone. In Dinornis the temporal fossa is Vf'ide 

 and deep, in Didus narrow and deep ; the alisphenoid is concave 

 where it ascends to coalesce with the mastoid, parietal and post- 

 frontal to form the temporal fossa : the limits of the orbitosphenoid 

 are also obliterated by a similar confluence ; in this region of the 

 skull the ' foramen ovale ' is preceded in Dinornis as in Didus by two 

 smaller foramina, and in front of these is the great ' foramen opti- 

 cum.' The parietals are very broad and short in both extinct genera; 

 but in Dinornis there is a median rising where the sagittal suture 

 originally ran, whilst Didus shows a depression and foramen here. 

 The mastoid in Dinornis, as in Otis, sends down two processes, one, 

 the tympanic process, short, — the other, or proper mastoid process, 

 long; this coalesces with the postfrontal in Dinornis, not in Otis : the 

 base of the mastoid has two articular cavities for the upper condyles 

 of the tympanic bone. In Didus the outer side of the mastoid is 

 convex, smooth, but with a slight oblique ridge ; it overhangs the 

 tympanic cavity, bending inwards, and sends a short compressed 

 pointed mastoid process in front of the anterior articular cavity for 

 the anterior and upper condyle of the tympanic. 



The presphenoid is a deep compressed plate, thickened and 

 rounded below ; the palatines abut against it, as in Didus, where 

 the fore-part of the pterygoids also rest in part upon the presphenoid. 

 The frontals of Dinornis form together a broad hexagonal plate 

 moderately convex, with the cerebral hemispheres indicated by very 

 slight risings: the postfrontals form the depressed lateral angles; the 

 anterior border is emarginate and coalesces with the nasals and pre- 

 maxillary, without being elevated above them. In Palapteryx the 

 frontals are more produced anteriorly before coalescing with the base 

 of the beak. In Otis the interorbital part of the frontals is deeply 

 and widely excavated. In Didus the frontals are broad and convex, 

 rising singularly above the cranial ends of the nasals and premaxil- 

 lary, with which they also coalesce. The supraorbital plate presents 

 a rough notch near the fore-part, where in Dinoriiis there is a shal- 

 low emargination. In Dinornis there is a shallow depression with 

 vascular grooves at the outside of the base of the postfrontal distinct 

 from the temporal fossa : in Didus the temporal fossa extends for- 

 wards above the postfrontal and forms there a reniform depression, 

 either for a gland, or what is less likel)^ for a co-extension of the 

 origin of the temporal muscle. The postfrontal is a strong trian- 

 gular obtuse process, ending freely as in Palapteryx, not joined to 

 the mastoid as in Dinornis. The orbitosphenoids, indicated by the 

 optic foramina, continue^the roof and septum of the orbits by coales- 



