I 2 2 S HUE ELD T. [Vol. XVII. 



and Nyctea scandiaca (all lacking ear-flaps), have perfectly 

 symmetrical auricular openings and crania. In all the other 

 groups, including seven species, the auricular apertures are 

 unequal in size or asymmetrical in other ways. On the two 

 last groups, which include Symium uralense, Syrnium lapponi- 

 cum, and Nyctala tengmalmi, the asymmetry is so pronounced 

 that even the cranium is more or less involved. 



This asymmetry of the auricular openings, their dermal 

 flaps, or the cranium, commonly exhibits itself as an anoma- 

 lism of the right side of the head, so the opposite or left side 

 in these must be regarded as the normal one. 



This anomalous condition in the majority of our species, so 

 far as the auricular openings and their dermal flaps are con- 

 cerned, consists in these strictures being larger and of greater 

 width on the right than on the left side. Where this condi- 

 tion also exists in the cranium, it is again the right side which 

 exhibits the anomalous development. It is only in Nyctala 

 tengviabni wherein we find that both sides present the con- 

 dition referred t€), and perhaps the most so upon the left side. 

 In the two species of Asio, where the irregularity is confined 

 to the dermal parts of the aural apertures, the right side must 

 again be regarded as the normal side. // would appear that in- 

 asmuch as the internal ear and the brain cavity are perfectly 

 symvietrical, neither of these parts enter into this anomalous 

 state of affairs. 



The six groups into which the North-European species fall 

 can be briefly characterized as follows : 



Group I. Dermal ear-flaps absent. Cranitim and auricular 

 openings sy7mnetrical. 



a. Jugal with an elevated osseous apophysis. 



I. SuRNiA FUNEREA (Linn.). 2. Glaucidium passerinum (Linn.). 



Auricular openings of medium size or small. Osseous crests on os 

 squamosum conspicuously individualized; viewed anteriorly they come 

 into plain sight at the posterior aspect of either orbit. Posterior periphery 

 of either orbit sharp where formed by the frontal bone. The greatest 



