W. P. PYCRAFT : BLACK-THROATED DIVER. 95 



on this head as may seem of interest to the readers of 

 British Birds. 



Circumstances recently placed in my way, at the 

 British Museum, a newly-killed Black-throated Diver, and 

 I immediately set to work to examine its Pterylosis, and 

 to compare the results of my examination with the figures 

 thereof which have from time to time appeared — all, 

 however, from Nitzsch. All these figures are inaccurate, 

 in showing that this bird presented extensive bare spaces, 

 or " apteria " on either side of the body, and along the 

 median line of the spinal tract between the shoulder- 

 blades : the under surface is not figured. But in the text 

 of Nitzsch's work {Eng. Trans., pub. 1867, Ray Soc, 

 p. 152), he says of the ventral aspect, "The inferior space 

 is very narrow, remains of equal breadth throughout, 

 and extends forward only to the furcula." This de- 

 scription is certainly inadequate. It is founded, apparently, 

 on an examination of two species — the Black- and Red- 

 throated Divers, and does not appear to fit either ! We 

 suspect, however, that here, as in so many other cases, 

 Nitzsch was working from dried skins for want of fresh 

 material, and this because he remarks that, " On the 

 pinion of the wing there are probably only ten feathers 

 .'..." In a freshly-killed bird these could easily have 

 been counted. 



Now let us turn to the facts, which, as may be seen 

 by a glance at the accompanying figures, in no way con- 

 firm Nitzsch's figures, or descriptions ; for this species of 

 the genus Colymbus at any rate, is even more closely 

 feathered than any of the Struthiones, which, so far, have 

 been commonly regarded as the most densely feathered 

 of all birds. 



The Apterium mesogastrcei is traceable only with diffi- 

 culty, and is represented by a very narrow space running 

 immediately under the free edge of the carina sterni, and 

 terminating with this, as may be seen in Fig, 1, the 

 apterium being indicated by the narrow blank space down 

 the middle of the breast. The Apterium tranci laterale 



