46 Mr. W. P. Pycraft on the 



III. Summary of Conclusions. 



Judged by pterylological characters alone, the position of 

 Photodilus, in the scheme proposed in my earlier paper, 

 seems to be most naturally along with the geuera which 

 make up the subfamily Asioninae, among which it stands as a 

 somewhat aberrant genus with leanings towards Asio. The 

 general conformation of the external ear is quite different 

 from that of any other Owl, but, externally, it may possibly 

 be regarded as more nearly like that of Asio than that of any 

 other genus. It is, indeed, possible that the external ear of 

 Photodilus approximately represents the primitive stage from 

 which the complex external ear of Asio has been derived. 

 The voluminous post-aural fold of the latter may very well 

 have arisen by the development of a fold of skin such as that 

 which supports the peripheral disc-feathers of Photodilus ; 

 but it is not easy to see how the operculum can have arisen. 

 It may be remarked, however, that even iu the nearly ripe 

 embryo of Asio there is no suggestion either of the post- 

 aural fold or of the operculum. 



In Photodilus, as will be seen in PI. II. figs. 1, 2, there 

 is little or nothing apparent which could give rise to such a 

 fold. It is possible, of course, that the operculum had its 

 origin in a raised fold such as that which forms the anterior 

 boundary of the auditory aperture in Photodilus. If we 

 assume this to be so, then it is possible that the membranous 

 rim bounding the aperture superiorly represents the mem- 

 branous fold which iu Asio runs from the post-aural fold to 

 the operculum and divides the " cavernum " into upper and 

 lower moieties. The transformation in the skull necessary 

 to convert the aural region of a bird like Photodilus into 

 that of Asio is not great, inasmuch as it could be accom- 

 plished by the shifting forwards and reduction of the post- 

 orbital process and the vertical extension of the bony 

 " cavernum."' 



In the general pterylosis of the body, Photodilus perhaps 

 comes nearest to Asio *. It differs therefrom in the 



* There is nothing whatever in the pterylosis of this bird which in any 

 way resembles that of Strix. Nitzsch, as Beddard has pointed out, seems 

 to have imagined that a resemblance of the kind existed. 



