204 Proceedings of the Royal Physiccd Society. 



to spread out broad, fan-shaped groups of these feathers on 

 either side of the head, which, as the figures show, impart 

 very striking characteristics to their physiognomy under 

 these circumstances. The feature, in less striking propor- 

 tions, is observable in a few other species. 



The Harpy affords also a good illustration of another type. 

 In this the feathers originating on ^A•hat (for want of a better 

 name) may be termed the parietal region of the skull, are 

 elongated in such a manner as to form a pair of postero- 

 lateral ov 2^ciTietal tufts (PL X., Figs. 2-6). These are capable of 

 erection at will, and they present, when half-raised, the form 

 of lateral crests — the edoes of the feathers on the crown of 

 the head forming a hollow between them. But the bird can 

 spread out each tuft as well as raise it, and is able, more- 

 over, to completely invert these feathers in such a manner 

 that their free ends are directed forward over the facial 

 region (PL X., Pig. 4). As the post-auricular tufts are usually 

 raised also at such times, the Harpy then presents as striking 

 a fioure as can be found throuohout the whole of the Sub- 

 Class Aves. Spizaetus coronatus resembles Tlirasaetus also in 

 this feature, and differs accordingly from all the normal 

 Spizaeti. 



In BicJiolophits, the (Jariamas (whose taxonomic position 

 is somewhere on the borders of the group under notice), there 

 is a well-developed median frontal tuft (PL X., Pig. 5), but 

 as the exact relationship of these birds to the Birds of Prey 

 has not yet been satisfactorily determined, I now pass it by 

 without further mention. At any rate, there is no such crest 

 amongst the acknowledged Birds of Prey. 



The remaining style of crest to be noticed is that already 

 well known under the name of occipital crest, from the region 

 of the skull where it originates. In nearly all cases this crest 

 is median in position, although the extent to which it is 

 developed laterally is subject to considerable variation. 

 There are several forms of occipital crest. One of these is 

 that of the heavy, wide, plume of rounded feathers displayed 

 upon the head of nearly all the genera of the Herpeto- 

 TiiERiN^. Helotarsiis, the Bateleur Eagle (PL X., Fig. 6), 

 Spilornis (PL X., Fig. Grr), and Polyhoridcs (PL X., Fig. (jh), 



