BIRDS OF NORTH AND MIDDLE AMERICA. 557 
Adult male.—Wing, 216-241 (232); tail, 112-132 (124); culmen, 
40-48.4 (44.7); depth of bill at base, 8-10.6 (9); tarsus, 19.2-21.6 
(20.2); middle toe, 26.5-28.9 (27.8).¢ 
Adult female.—Wing, 212-246 (229); tail, 111-129 (121); culmen, 
37.1-42.4 (42.2); depth of bill at base, 7-10.2 (8.4); tarsus, 18.1- 
20.5 (19.7); middle toe, 25-29.5 (27.5).° 
Off Pacific coast of Central America, breeding on Clipperton and 
Cocos Islands. 
Micranous diamesus HELLER and SNoperass, Condor, iii, May, 1901, 76 (Cocos 
Island; coll. Leland Stanford Jr. Univ.).—Snopcrass and HELLER, Proc. 
Wash. Acad. Sci., iv, 1902, 509 (Cocos and Clipperton islands; descr.; crit., 
measurements).—GiFForD, Proc. Calif. Acad. Sci., 4th ser., ii, pt. i, 1913, 
29 (breeding on Clipperton and Cocos islands; habits, measurements, etc.), 
113 (measurements). 
Megalopterus minutus diamesus MatHews, Birds of Australia, ii, pt. 4, Nov. 1, 
1912, 423. 
Genus GYGIS Wagler. 
Gygis (not Gyges Bory de St. Vincent, 1825) Wacter, Isis, xxv, 1832, 1223. 
(Type, by original designation and monotypy, Sterna candida Gmelin= 
S. alba Sparrman.) 
Leucanous © Matuews, Birds Australia, ii, pt. 4, Nov. 1, 1912, 432, in text. 
(Type, by original designation, Gygis microrhyncha Saunders.) 
Alphagygis¢ Matuews, Austral. Avian Rec., ii no. 5, Sept. 24, 1914, 110. 
(Substitute for Gygis Wagler, 1832, considered as preoccupied by Guges 
Bory de St. Vincent, 1825.) 
Rather small Sternide (wing 218-251 mm.) with wholly white 
coloration, cuneate, straight-tipped bill, deeply excised webs, and 
tail both forked and graduated. 
Bill about as long as head, compressed and cuneate terminally 
and relatively deep basally; exposed culmen longer than tarsus and 
« Twenty-six specimens. 
b Thirty specimens. 
Depth A 
‘ Cul- . Middle 
Locality. Wing.| Tail. of bill | Tarsus. 
men. | at base. toe. 
MALES. 
Sixteen adult males from Clipperton Island........... 230 123 44.1 9.4 20.3 27.5 
Ten adult males from Cocos Island...............----- 233 124 45.3 8.6 20 28 
FEMALES. 
Twelve adult females from Clipperton Island.........- 227 121 41,9 8.7 19.7 27.3 
Eighteen adult females from Cocos Island............. 231 120 42.4 8 19.6 27.6 
(The above measurements are from Gifford, Proc. Calif. Acad. Sci., 4th ser., ii, pt. i, 
1913, 32, 113.) . 
© Aeuxds, white+Anous (avous, foolish). (Mathews.) 
4 “Adda, first-+Gygis (vyivns, a fabulous bird); Mathews. 
