460 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 
dd. Frontal feathering forming a straight line across base of culmen; gonys 
longer than mandibular rami; a slender, recurved, auricular plume on 
each side of head; under parts dark-colored. 
Larosterna (extralimital).¢ 
bb. Tail both forked and graduated, the lateral rectrices much shorter than the 
longest, sometimes shorter than middle pair. 
ce. Lateral rectrices shorter than middle pair; middle toe, without claw, much 
shorter than exposed culmen; coloration sooty above and below, only the 
pileum and hindneck (wholly or in part) white or gray. 
d. Gonys shorter than mandibular rami; tail more graduated, the lateral 
rectrices conspicuously shorter than middle pair, the third or fourth 
pairs (from outside) longest .......-.-.-----+--+---- Anous (p. 544). 
dd. Gonys much longer than mandibular rami; tail less ‘graduated, the 
lateral rectrices not conspicuously shorter than middle pair, the 
second, or second and third, pairs (from outside) longest. 
Megalopterus (p. 552). 
cc. Lateral rectrices longer than middle pair; middle toe, without claw, longer 
than exposed culmen; coloration bluish gray, paler on head, neck, and 
under parts....... Procelsterna (extralimital).> 
aa. Tarsus not longer than first two phalanges of middle toe, only about one-nine- 
teenth as long as wing, less than one-third as long as exposed culmen, the latter 
straight to the acute (sometimes slightly recurved) tip; webs between anterior 
toes deeply incised; coloration wholly white (except shafts of remiges and 
rectrices). Gygis (p. 557). 
Genus HYDROPROGNE Kaup. 
Hydroprogne Kaur, Skizz Entw.-Ges. Eur. Thierw., 1829, 91. (Type, as desig- 
nated by Gray, 1846, Sterna caspia Pallas.) 5 
| Sylochelidon Bream, Vég. Deutschl., 1831, 767. (Type, by original designa- 
tion, Sterna caspia Pallas.) 
Helopus WaGuer, Isis, 1832, 1224. (Type, by original designation, Sterna caspia 
Pallas.) 
Pontochelidon Hoac, Edinb. New Philos. Journ., xli, no. 81, July, 1846, 55, 69. 
(Type, as designated by Mathews, 1915, Stone caspia Pallas; see Mathews, 
Austral Avian Rec., ii, 1915, 133.) ; if 
Heroprogne BULLER, Suppl. Birds New Zealand, i, 1908, 157. (Misspelling only.) 
Very large (the largest of) Sternide (wing 400-423 mm.) with 
large, stout bill, slightly forked tail, and with occipital feathers 
elongated but blended (not lanceolate). 
Bill relatively large and very stout, its depth at base equal to nearly 
half the distance from anterior end of nostril to tip of maxilla or 
nearly one-third the length of exposed culmen, the latter about as 
long as combined length of tarsus and first two phalanges of middle 
@ Naenia, (not Nenia Stephens, 1829) Boie, Isis; 1844, 189 (type, by monotypy, 
Sterna inca Lesson).—Sternolophota ‘Lesson,’ Bonaparte, Compt. Rend., xliii, no. 
21, Nov., 1856, 993.—Larosterna Blyth, Cat. Birds Mus. Asiat. Soc., 1849 (1852), 
293 (type, by monotypy, Sterna inca Lesson).—Jnca (not of Lepeletier and Serville, 
1825) Jardine, Contr. Orn., 1850, 33 (type, by tautonymy, Sterna inca Lesson). 
Coasts of Chile and Peru. (Monotypic.) 
b Procelsterna Lafresnaye, Mag. de Zool. (2), Ois., pl. 29 and descr. (type, P. 
tereticollis Lafresnaye—Sterna cxrulea F. D. Bennett). 
Southern Pacific Ocean, north to Hawaiian group. (Three species.) 
* 
