716 SHUFELDT—OSTEOLOGY OF THE STRIGES. [Dec. 7, 
especial advantage it can bestow upon the bird, or how it would 
better fit it for the struggle for its existence. Apparently the largest 
and most powerful Owls in the world have perfectly symmetrical 
crania; while, as I have already noted above, the largest species 
known to me wherein evident asymmetry is present in that part of 
the skeleton is Syrutum cinereum. On the other hand, our very 
smallest owls, the pygmies of the group, as Glaucidium and Micro- 
pallas (see Pl. XIV, Figs. 17 and 18), possess wonderfully symmet- 
rical little skulls, barely exceeding in size the skull of a large 
Thrush. 
Other ornithologists have invited our attention to this cranial 
asymmetry as exemplified by the genus Vyc/a/a. As long ago as 
1870 Dr. T. H. Streets, of the United States Navy, referred to it in 
the Proceedings of the Academy of Natural Sciences of Philadelphia 
(p. 28); and in the A/zstory of North American Birds, Mr. Ridgway 
has figured the skull of Richardson’s Owl (VW. vichardsonz), showing 
the same character. 
Nyctea nyctea (see Pl. XII, Figs. 8 and 11; Pl. XVI, Figs. 26, 
28 and 29) has a skeleton that in all essential particulars closely re- 
sembles that part of the anatomy of Luwbo virginianus. The bird 
clearly belongs to the bubonine section of the group. 
Screech Owls, or what we call the Screech Owls in the United 
States, are of many species and subspecies in the fauna. ‘They have 
had the genus Jegascops created to contain them, and I have ex- 
amined complete skeletons of a number of the varieties. After the 
bubonine order in point of skeletal structure, they yet exhibit some 
interesting little peculiarities of their own. (See Pl. XIII, Figs. 12 
and’ 16); Ply XV, Fig. 19.) 
Megascops asto trichopsts (or any of its genus) has a skull more 
like that part of the skeleton in Sfeofyfo than any other of our Owls, 
with the exception of Surnza. It differs, however, in possessing a 
well-developed vomer, whereas it lacks the process on the quadrato- 
jugal bar seen in the Burrowing Owl. AVegascops has an extensive 
internasal septum which is quite thick and extends well backward. 
The interorbital septum is thin, and may show a small vacuity near 
its centre. Either superior border is but very slightly rounded off, 
it being quite sharp in Sfeotyfo. Another point wherein these two 
Owls agree and differ from others is the formation of the foramen 
in the squamosal region of the cranium, through which the tendon 
of the temporal muscle passes. ‘This character was described when 
