232 MR. J. H. GURNEY ON A SPECIMEN OF POLYBORUS. [Feb. 19, 



and oii the interscapular feathers. All these shaft-marks resemble 

 greatly in shape those on the corresponding portions of the plumage 

 in the normal immature P. tharus; but in the latter the shaft-marks 

 are paler than the sides of the feathers, while in the pale Patagoniau 

 specimen they are darker and more rufous. In the last-named bird 

 faint transverse marks of a similar rufescent tint, but very pale, are 

 perceptible on the abdomen and under tail-coverts ; similar transverse 

 marks, but darker, less rufous and more numerous, are apparent in 

 a specimen of P. tharus in Messrs. Salvin & Godman's collection, 

 marked " Bolivia ?," which seems to me to be passing from the im- 

 mature to the adult stage. Transverse bars alternately dark and pale 

 and of a similar character are found on the lower part, of the back in 

 Polyborus tharus in all its stages ; and these markings, though 

 modified in their coloration, especially by the substitution of dull 

 fulvous bars for those of blackish brown in ordinary specimens, are 

 unmistakably present in the pale specimen under consideration. 



The latter bird was moulting its primaries when it died ; and I 

 observe that the transverse bars on the new quill-feathers are broader 

 than on the old, the latter agreeing in general character with the 

 corresponding bars in immature specimens of the normal P. tharus, 

 and the former with the same bars in adult birds. These bars are 

 much more rufous, especially on the newly acquired feathers, than 

 is the case in normal specimens ; in the latter they are of various 

 shades of brown, but not tinged with rufous. 



The narrow transverse bars on the upper surface of the tail are 

 less distinct in the Patagonian pale bird than in ordinary specimens 

 of P. tharus ; but they are similar in character and of about the same 

 number (from 1 5 to 1 6). The broad terminal blackish-brown band at 

 the end of the tail in the ordinary bird is represented in the pale 

 one by a dull fawn-coloured band of similar dimensions tinged with 

 rufous on its upper edge and on the external webs of the outer pair 

 of rectrices l . 



During a recent visit to the Zoological Society's Gardens, I observed 

 that the bare skin on the face of the survivor of the two pale birds, 

 changed rapidly from carmine-red to pale pink ; but Mr. Bartlett 

 informed me that in neither of the pale specimens did these occasional 

 and transient changes assume a wider range, and that in them the 

 bare skin never became yellow, as may be sometimes seen to be the 

 case (even to the extent of a decided lemon-colour) in the normal 

 specimens of Polyborus tharus inhabiting the adjacent cages. 



On the whole, I incline to agree with the opinion expressed by 

 Mr. Sclater in his original notice of this curious pair of birds, that 

 they are " young individuals of P. tharus in an abnormal phase of 

 plumage," or, as I would rather say, of colouring generally. 



1 The tail in .the pale birds was imperfect when they were drawn for the 

 plate in the Proc. Zool. Soc. ; but the specimen under consideration obtained its 

 full tail subsequently. 



