128 SHUFELDT. [Vol. XVII. 



similar to what occurs in S. ahico, but the difference between 

 the two sides is, strangely enough, upon the whole, less decided 

 than in the last-named species, although always noticeable. It 

 is here likewise that it is the right side wherein the auricular 

 openings and ear-flaps are the larger. The asymmetry of the 

 cranium is similar in either species, owing to a peculiar struc- 

 ture of the right osseous crest of the os squamosum, which is 

 the case in a more marked degree in 5. lapponicmn than it 

 is in S. tiralense. In the last-named species the asymmetry is 

 but feebly pronounced, although always present ; the osseous 

 crest of the os sqiiamosiim is somewhat more produced for- 

 wards upon the right side, but nevertheless does not quite 

 come in contact with the hinder border of the alisphenoid. 

 On the other hand, this is the case in 5. lapponicmn ; the 

 osseous crest is more lofty and wider, and extends its superior 

 margin quite to the above-named bone, with which it coosifies. 

 At the same time the entire right side of the head is more 

 drawn out laterally, and exhibits a greater vertical compres- 

 sion than it does upon the left side, and this is especially to 

 be observed when the cranium is viewed upon its anterior 

 aspect. In both these species the orbital cavity is compara- 

 tively small, and the interorbital septum low and thick, which 

 is especially the case in ^. lapponicum. 



In the last-named species the cranium is, upon the whole, 

 smaller as compared with the beak than it is in any other 

 species, and this, notwithstanding the fact that the beak is 

 not very powerfully developed, as it is, for example, in Bubo 

 and Nye tea. 



Group VI. Ear-flaps present. Cranium deeidedly asymmet- 

 rieal. Auricular openings wide, icniform in size, and 

 together with the earflaps exhibiting an asymmetry agree- 

 able with that of the cranium. 



lo. Nyctala tengmalmi (Gmel). 



Auricular openings very wide, with crescent-formed ear-flaps ; Asym- 

 metry of aural entrance agreeing with that of the cranium. Osseous crest 

 of OS squamosu}n large, deep, and distorted upon both sides ; especially 



