1 88 PATAGONIAN EXPEDITIONS I ZOOLOGY. 



Sterna maculata, Vieill. N. Diet. d'Hist. Nat. XXXII. p. 176 (1819: ex 



Azara). 

 Sterna argentea, Hartl. Ind. Azara, p. 26 (1847); Burm. Reis. La Plata, 



II. p. 419 (1861 : Rio Parana). 



FIG. 113. 



Sterna superciliaris. Adult male. Natural size. From material in British Museum. 



GENERAL DESCRIPTION. 



Size. Adult (breeding). Total length, 9 inches. 



Wing, 7.25 inches. 



Tail, 3.25 inches. 



Tail (depth of fork), 1.3 inches. 



Culmen, 1.5 inches. 



Tarsus, 0.65 inches. 



Color. Adult (breeding). Above, mantle, wings and neck rather dark 

 pearl grey. A black cap on head. Below pure white. 



Head : With a black cap extending from forehead back to nape, and on 

 sides of head to a line even with the lower eyelid. Forehead white, 

 extending back in a broad band to the middle of the upper eyelid. (See 

 cut 113.) The lores white, divided by a narrow black streak reaching 

 from the eye to upper part of the upper mandible. The remainder of 

 sides of head and face white. 



Neck: Deep pearl grey above, shading gradually on the sides into 

 white ; below pure white. 



Back : Mantle, rump and upper tail coverts deep pearl grey. 



Wings : Deep pearl grey, with a brownish tinge on the inner second- 

 aries. ^\\tfour outer primaries, almost wholly dusky black, with narrow 

 white margins on the inner webs of the first two, and very little white on 

 the third and fourth. 



Tail : Like back, but with faint whitish edging to each feather ; the 

 streamers paler and with a greater inclination toward whitish. 



