558 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



middle toe without claw (sometimes much longer thnn combined 

 length ot tarsus and middle toe vnth claw), nearly straight through- 

 out, but slightly depressed immediately above nostril and more or 

 less elevated basally; gonys longer than mandibular rami, ascending 

 terminally; nostril rather narrowly elliptical, longitudinal, rather 

 small, situated in advance of mental antia and separated from nearest 

 loral feathering by a space much gi eater than length of nostril; 

 anterior outline of feathermg on forehead and lores variable; in 

 G. alba sometimes forming a frontal antia or projectmg angle on base 

 of culmen and sloping thence backward and downward to rictus, but 

 sometimes, as in G. microrhynclta, forming a notch or reentrant 

 angle at base of culmen, with a distinct antia (latero-frontal) on each 

 side. Wing long and pointed, with longest primary exceeding distal 

 secondaries by less than twice the distance from tips of the latter to 

 bend of wing; outermost primary longest in G. alba, slightly shorter 

 than the next in G. microrhyncha. Tail less than half as long as wing 

 (much less in G. microrJiynclia), both forked and graduated with next 

 to outer pair of rectrices longest, the middle pair of rectrices much 

 shorter than the outermost and all the rectrices acuminate m G. alba, 

 but as long as or slightly longer than the outer and all the rectrices 

 broader and less acuminate termmally in G. microrhyncha. Tarsus 

 about as long as combined length of first two phalanges of middle 

 toe; outer toe decidedly shorter than middle toe; webs deeply 

 excised, occupying only about haK the interdigital spaces. 



Plumage and coloration. — Plumage soft and blended. Color, 

 entirely white, except a narrow black orbital ring and brownish 

 shafts to primaries and (sometimes) rectrices. 



Range. — Pacific, Indian, and southern Atlantic oceans. (Two 

 species.) 



KEY TO THE SPECIES OP GYGIS.o 



a. Bill much stouter, its depth at base equal to about one-fourth the length of exposed 

 culmen; tail nearly half as long as wing, deeply forked, the outermost rectrices 

 much longer than middle pair, all, except middle pair, distinctly acuminate; 

 shafts of primaries and rectrices distinctly brown or dusky. (Intertropical 

 portions of Pacific, Indian, and southern Atlantic Oceans) . . . Gygis alba (p. 559). « 



« Mr. Gregory Mathews divides this species into the following geographic forms or 

 subspecies: 



(1) Gygis alba alba. — Sterna alba Sparrman, Mus. Carls., fasc. i, 1786, no. 11 ("India 

 orientali, ad promontorium Bonae Spei Insulas que maris pacifici);" Mathews, 

 Bds. Austr. ii, p. 4-11, designates Ascension Id., as type locality); Gmelin, Syst. Nat., 

 i, pt. ii, 1789, 607; Latham, Index Oni., ii, 1790, 808. — G[/gisulba Sharpe, Ibis, 1904, 

 217 (South Trinidad I.). — Gygis alba alba Mathews, Birds Australia, ii, pt. 4, Nov. 1, 

 1912, 442 (Fernando Noronha; Ascension Island; South Trinidad Island). — Gygis 

 Candida (not Sterna Candida Gmelin, 1789) Melliss, Ibis, 1870, 106 (St. Helena, breed- 

 ing); Saunders, Proc. Zool. Soc. Lond., 1876, 667, part (monogr.); 1877, 797, part 

 (Ascension I.); 1880, 163 (Trinidad I.); Cat. Birds Brit. Mus., xxv, 1896, 149, part 



