558 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
middle toe without claw (sometimes much longer than combined 
length ot tarsus and middle toe with 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 gteater than length of nostril; 
anterior outline of feathering on forehead and lores variable; in 
G. alba sometimes forming a frontal antia or projecting angle on base 
of culmen and sloping thence backward and downward to rictus, but 
sometimes, as in G. microrhyncha, formimg 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. microrhyncha), 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 in @. alba, 
but as long as or slightly longer than the outer and all the rectrices 
broader and less acuminate terminally 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 half 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 
1 
species.) 
KEY TO THE SPECIES OF GYGIS.4 
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). 
4 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. 441, designates Ascension Id., as type locality); Gmelin, Syst. Nat., 
i, pt. li, 1789, 607; Latham, Index Orn., ii, 1790, 808.—Gygis alba Sarre, 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 
