714 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



itnd shallow transverse, slightly curved (distally convex) grooves, the 

 mandible usually with one or two similar but more vertical grooves. 

 Wing moderate, the longest primary (outermost) exceeding distal 

 secondaries by more than half the length of wing. Tail about two- 

 fifths as long as wing, graduated for more than one-third its length, 

 the middle rectrices obtusely pointed; rectrices 12. Tarsus about 

 as long as chord of exposed culmen, the acrotarsium continuously 

 transversely scutellate; middle toe, without claw, much longer than 

 tarsus, the outer toe as long as middle toe (but its claw smaller), the 

 inner toe (without claw) as long as first two phalanges of middle toe. 



Plumage and coloration. — Plumage of head, especially the anterior 

 portion, short, very dense, and soft or velvety. Upper parts sooty 

 black, the secondaries narrowly tipped with white; under parts 

 immaculate white. In breeding season, the head and upper neck 

 dark sooty brown (deepening into blackish on pileum and hindneck), 

 relieved by a white line from eye to base of cuhnen. 



Range. — Coasts and islands of the northern Atlantic Ocean, south 

 in winter to Atlantic coast of United States, Mediterranean Sea, etc. 

 (Monotypic.) 



ALCA TORDA Linnaeus. 



RAZOR-BILLED AUK. 



Adults in breeding season (sexes aUke). — Head and upper neck 

 plain dark brown (bright clove brown or deep olive-brown), becoming 

 much darker on pileum and gradually darkening into slate-black on 

 hindneck and rest of upper parts; secondaries narrowly but sharply 

 tipped with white; a narrow wliite line extending from anterior angle 

 of eye to near base of culmen; under parts, including axillars and 

 under wing-coverts, immaculate white, this extending forsvard to and 

 including the lower foreneck; bill black, with one or more of the 

 transverse grooves whitish; interior of mouth yellow; iris dark 

 brown; legs and feet dull black. 



Winter plumage. — Whole under portion of head and neck and 

 space behind auricular region white; no white line between bill and 

 eye; bill without the basal lamina; otherwise as in summer. 



Young. — Similar in coloration to the winter adult, but biU smaller 

 and without grooves. 



Downy young. — Head, neck, and under parts plain dull whitish, 

 usually more or less tinged above with brownish buff; back, rump, 

 and flanks varying from pale brownish buff, more decidedly brownish 

 posteriorly, to dark sooty brown, the down dusky immediately beneath 

 the surface; posterior and lateral under parts more or less tinged 

 with brownish buff or sooty brownish. 



