18 R. W. SHUFELDT, 
rest of the skull, with the floor of the meatus fairly performed in 
bone. Above, to a little extent and posteriorly entirely, the tympanic. 
periphery is extended on to the large, inferiorly produced tympanic 
plate of the exoceipital, terminating at its postero-inferior apex 
below. All of this well shown in Fig. 12 of Plate 3, and a similar 
conformation of this part of the skull is found in Chen hyperboreus; 
Cereopsis (Fig. 11); Swans of the genus Olor; other Geese of the 
genus Chen, and identically the same in Branta (Fig. 19); very 
nearly the same in Oidemia perspicillata, the only difference here 
being that the tympanic plate of the exoceipital extends rather 
more posteriorly, a difference which, in Harelda, is even better 
marked (Fig. 66, Pl. 9), while at the same time, the floor of the 
meatus is more extensively ossified.. What we find in Harelda 
hyemalis is repeated in Charitonetta albeola, Spatula, and several other 
species of ducks. In Chaulelasmus the aural aperture is small, 
subeircular in outline, the floor of the meatus entirely ossified, and 
the exoceipitai plate much produced posteriorly (Fig. 32, Pl. 6). 
Still other Anatinae have the meatal floor complete and produced 
well outwards, — the free external margin being bent upwards. 
This modification is best seen in Anas platyrhynchos and A. rubripes;z 
Tachyeres cinereus; Marila collaris and in other species. 
As I have elsewhere pointed out, the interorbital septum 
in the skulls of Anatidae rarely presents any vacuities, while in 
Dendrocygna such foramina seem to occur more or less frequently. 
When present, it is, without exception — so far as Il am aware — 
a single foramen or vacuity as shown in Fig. 12 of Pl. 3, and 
Fig. 44 of Pl. 8. Most adult ducks and geese commonly exhibit in. 
the interorbital septa of their skulls the three usual foramina shown 
in the skulls presented in Fig. 27 (Pl. 5) and 38 (Pl. 6). 
Comparatively few of the Anseres ever seem to have the 
pars plana developed in bone. Of the large array of skulls of 
the representatives of the group under consideration before me at 
this writing, I only find it very large and completely developed, on 
either side, in Erismatura jamaicensis (No. 11220, U. S. Nation. Mus.), 
and equally as extensive in Dafila acuta (No. 4989, U. S. Nation. Mus.). 
In the speeimen of Erismatura, the lacrymal is a very large, thin, 
quadrilateral lamina of bone, entirely lacking in processes, and which, 
in the adult, coossifies mesially with the big and somewhat spongy 
pars plana. In some other Anseres, the partes planae are 
sceroll-like and more or less deficient in function, as in Anas rubripes, 
