744 GEOLOGICAL SURVEY OF THE TERRITORIES. 
aspect in the skulls of our Cathartide from this locality as far back as 
the well-defined line limiting muscular attachment on the posterior 
aspect of the cranium and between the upper boundaries of the orbits. 
The surface of the skull presents a very evenly distributed convexity, 
it being most decided as it slopes away over the auricular entrances 
on either side. The median groove, present in so many of the clase, 
is absent. The surface exhibits many osseous venations, the majority 
of which run to the foramina that exist in an irregular double row, 
removed by a few millimeters from the orbital peripheries. These fora- 
mina lay along in a shallow groove in these localities. From them 
the bony and sharp-edged brows overhang the orbital cavities below 
to a greater or less degree; we say for a greater or less degree because 
this is one of the characteristics of the skulls of these birds that seem to 
vary in every individual and in every species. As a prominent instance, 
look at the two ecrania of Pseudogryphus that we have before us; in one 
the superior orbital peripheries are jagged and thin, coming very close 
to the row of foramina described above, being only a little over 2 centi- 
meters apart, measuring between points in the two lines that are the 
nearest together, while in the other they are rounded and arched over 
the orbital cavities, thick and heavy, the edges being nearly 5 centi- 
meters apart, lending to the general aspect of the skull a far more 
raptorial look, as the osseous brows are thus made to be permanently 
arched and overhanging. This variance in the integrity or complete- 
ness of the vaults of the orbit may be due to the age of the specimen— 
the older the individual the more complete the roof of his orbit may 
be; but we have nothing to offer to sustain any such theory. 
Ridgway in his “Outlines of a Natural Arrangement of the Falcon- 
ide” {read before the Philosophical Society of Washington, April, 1875] 
gives us some very interesting and valuable studies upon the lacrymal 
and its superciliary process as found among these genera, illustrating 
his remarks with very good outline drawings of the species treated. 
We find that the lacrymal is subject to a great many changes as to its 
form, its method of articulation, the bones it comes in contact with, and 
soon. As these changes are quite constant for the species where they 
occur, they become valuable as points of distinctive differences tor - 
diagnostic purposes. Among the majority of the Hawks and Hagles the 
superciliary process stands out from the head, at a varying angle for 
different species, and may have articulating with its extremity an ‘‘ac- 
cessory piece” (Harpagus bidentatus). 
In Merastur brachypterus so long and prominent has this supereil- 
iary process become, that, aided by the intervening membrane, it makes 
up the major part of the orbital vault. 
In Polyborus auduboni we find the body of the bone, freely articu- 
lating with the entire border of the wing of the ethmoid and three- 
fourths of the inner margin of the supercilary process, freely, though 
very intimately, meeting the frontal and nasal; the membranous inter- 
space being limited. 
The next interesting step we observe in the cranium of Gypogeranus 
serpentarius, where the superciliary process forms much the larger share 
of the entire bone, while the body becomes a mere inbent osseous bar 
that touches the ethmoidal wing at the angle. Here the inner border 
of the superciliary process meets the nasal and frontal segments for its 
wos length; the union being very close, but the suture plainly vis- 
ible. 
In Neophron perenopterus the arrangement leans more towards the 
Faleonide than towards the Cathartide, though there is a positive step 
