Recent Literature. 91 



below. The fall of this large piece exposes the mental matrix, and a mem- 

 branous triangular space, susceptible of being retracted or drawn in. 

 This is the Triangle of atrophy (le Triangle atrophique) to which special 

 attention should be paid. 



The strangest change is certainly that produced in the depth and shape 

 of the lower mandible. In the adult, in spring, the base of the lower 

 mandible is produced (downward and backward), and the outline of the 

 gonys is a regular curve. In winter the base is narrowed or constricted, 

 and the lower border forms two straight lines meeting at an angle. It 

 looks as if the lower corner of the bill had been chopped off; and the way 

 this comes about is as follows : Loss of the mental buckler exposes the 

 yellowish membranous " triangle of atrophy," which gradually shrinks, 

 and is withdrawn into the fossa formed by the slight divergence of the 

 forks of lower jaw (i. e. into the interramal space). In some speci- 

 mens the process of retraction is not accomplished at once ; for after the 

 loss of the mental buckler, the atrophic triangle is often covered with a 

 delicate horny pellicle which exfoliates and soon falls. This disappearing 

 triangle can only be studied on the living subject ; and ornithologists 

 should be on their guard lest they fall into error in examining speci- 

 mens in course of transformation, either after complete drying or before 

 the secondary and final exfoliation just mentioned. In default of exami- 

 nation of the living subject a good idea may be gained by getting a speci- 

 men in full breeding array, with a bill so thin as to be translucent at this 

 part. In a very favorable specimen in the author's possession examined 

 by transmitted light, the bony part of the jaw formed the shadow, the 

 atrophic space the penumbra, while the horny tip was translucent. It is 

 supposed that such specimens might easily be secured in April or early 

 May, before the horny pieces are fully developed. Another good way, 

 open to any one, is to remove the horny sheath of the mandible by pro- 

 longed maceration ; when the atrophic part, thus uncovered and softened, 

 is seen in its normal condition. The horny sheath of either mandible 

 will come off whole by maceration, — the separation of the several pieces 

 of which it is composed being a vital process only accomplished at the 

 time of the moult. 



The commissural rosette, in spring a thick naked rugous skin of a 

 beautiful orange-color, afterwards wastes away and turns pale. The 

 transformations of the parts about the eye seem very simple after what 

 has gone before. The red border of the lids shrinks and loses color. The 

 horny protuberances fall off, leaving a naked skin which rapidly shrinks 

 and disappears. 



The author concludes this remarkable paper with some pertinent and 

 suggestive observations on other species of Fratercula, and on Lunda cir- 

 rhata. — Elliott Coues, Washington, March 15, 1878. 



