The Zoologist — August, 1870. 2251 



do. 1*30; inner do. MO; culmen -75; rictus -90 ; gonys '60 ; depth 

 of bill opposite posterior extremity of nostrils '40 ; width '30. 



As regards colour, this species is remarkably constant. Hardly any 

 other differences than those first noticed are to be found, after examina- 

 tion of extensive series ; and they may all be summed up as merely 

 varying shades of the same colour, and slight variation in its extent 

 downwards upon the breast. The bill at all ages and seasons presents 

 its peculiar parti-coloration. These remarks, however, probably do 

 not apply to fledglings. As regards size, the species is perhaps 

 unusually variable, as may be seen by the measurements given above, 

 which represent extremes in those cases where two sets of figures are 

 given, and the average in other measurements. The bill, in particular, 

 is liable to great variation both in length and in stoutness. Some 

 bills are very large and robust, nearly as wide as high at the base, 

 rather obtuse at the tip, and with decidedly curved culmen and gonys ; 

 others are longer in proportion to their transverse dimensions, 

 decidedly compressed throughout, acutely pointed, with almost 

 straight culmen and gonys. The corrugations about the base of the 

 upper mandible are sometimes nearly obsolete, and when present are 

 very variable in character. Very likely they are hardly, if at all, 

 apparent in life; for they seem to be produced mainly by the 

 shrinking in drying of the skin covering the nasal fossae and base of 

 the culmen. All the variations exhibited by the numerous specimens 

 seem to be merely individual differences, and are not sufficient to 

 excite a suspicion that more than one species is represented in the 

 series. 



Mergulus Cassinii, Gambel (Arctica Cassinii, Gray), is now well 

 known to be this species, first described by Pallas, as above quoted. 

 The species has no other synonyms of consequence. Its striking 

 peculiarities suffice to prevent misconception regarding it. 



Subfamily Urin^. — Mergulus {Ray), Vieill. 

 Bill very short, culmen only three-fourths the tarsus, very stouf^ 

 scarcely compressed, obtuse at the tip, as wide as high at the base, 

 the sides of both mandibles convex or vaulted, the tomial edge of the 

 upper greatly inflected, the culmen very convex in outline, with a 

 broad flattened ridge, the rictus ample, much decurved towards the 

 end, the gonys straight, very short, the inferior mandibular rami 

 correspondingly elongated, widely divaricating, the inlerramal space 

 very broad, the nasal fossae short, wide, deep, partially feathered. 



