ALCIDJE — THE AUKS — FRATERCULA. 5zo 



extreme base ; gonys convex toward the base, straight, or even sometimes slightly concave, for 

 the terminal half, or more; deciduous nasal shield becoming rapidly narrower toward the top; 

 terminal portion of the bill transversely sulcate ; base of the maxilla surrounded by a deciduous 



thickened horny rim, and rictus ornamented by a deciduous tumid rosette ; eyelids furnished with 

 deciduous horny plates. No tufts about the head in the breeding-season. 



F. arctica. 



The deciduous accessory pieces of the bill, together with the rictal and palpebral ornaments, 

 are cast at the close of the breeding-season. 1 

 Following is a key to the known species. 



1. F. arctica. Horny process of upper eyelid short, subcorneal ; grooves of the bill very 



oblique, broad, and distinct, the deciduous shields occupying not more than the basal 

 half of the bill. Chin and whole throat grayish. 



a. arctica. Bill and general size smaller. Oilmen, 1.60-1.90 inches ; gonys, 1.40-1.80 ; 

 depth of maxilla at base, .75-90; of mandible, .40-.50 ; tarsus, 1.00-1.10 ; middle toe, 

 without claw, 1.25-1.40. Wing, 6.00-6.50. Hah. Coasts of the North Atlantic, from 

 Southern Greenland southward. 



(3. ylacialis. Bill and general size larger. Oilmen, 2.00-2.30 inches ; gonys, 1.40-1.60; 

 depth of maxilla at base, .85-1.00 ; of mandible, .70-.80 ; tarsus, 1.10-1.35 ; middle toe, 

 without claw, 1.45-1.60. Hah. Arctic Ocean, from Spitzbergen to northern and western 

 Greenland ; probably also western shores of Baffin's Bay, and Northern Labrador. 



2. F. corniculata. Horny process of upper eyelid narrow, elongated, horn-like ; grooves of 



bill nearly vertical, narrow, and less distinct ; deciduous shields occupying much more 

 than the basal half of the bill. Whole throat blackish, only the chin gray. Hob. Coasts 

 and islands of the North Pacific and Behring's Sea. 



1 See Dr. Louis Bureau : De la Mue dn Bee ft des Ornements Palpebraux <lu Macaroux arctiquc, 

 Fratercula arctica (Lin.), Steph., apres la Saison des Amours (Ball. Soc. Zool. de France, 1878, pp. 1-21, 

 pis. iv. v.). 



