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).o 



hh. Tail both forked and graduated, the lateral rectrices much shorter than the 



longest, sometimes shorter than middle pair. 



c. 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 out:side) 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).f' 



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 Kaup, Skizz Entw.-Ges. Eur. Thierw., 1829, 91. (Type, as desig- 

 nated by Gray, 184G, Sterna caspia Pallas.) 



Sylochelidon Brehm, Vog. Deutschl., 1831, 767. (Type, by original designa- 

 tion, Sterna caspia Pallas.) 



Helopus Wagler, Isis, 1832, 1224. (Type, by original designation, Sterna caspia 

 Pallas.) 



Pontochelidon Hogg, Edinb. New Philos. Journ., xli, no. 81, July, 1846, 55, 69. 

 (Type, as designated by Mathews, 1915, Sterna caspia Pallas; see Mathews, 

 Austral A\ian Rec, ii, 1915, 133.) 



Eeroprogne Buller, Suppl. Birds New Zealand, i, 1905, 157. (Misspelling only.) 



Very large (the largest of) Sternidte (wing 400-423 mm.) with 

 large, stout bill, shghtly 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 



a Naenia (not Naenia 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, Gat. Birds Mus. Asiat. Soc, 1849 (1852), 

 293 (type, by monotypy. Sterna inca Lesson). — Inca (not of Lepeletier and Serville, 

 1825) Jardine, Gontr. Orn., 1850, 33 (type, by tautonymy, Sterna inca Lesson). 



Coasts of Chile and Peru. (Monotypic.) 



b Procelsterna Lafresnaye, Mag. de Zool. (2), Gis., pi. 29 and descr. (type, P. 

 tereticollis Lafresnaye =6'<erna caerulea F. D. Bennett). 



Southern Pacific Ocean, north to Hawaiian group. (Three species.) 



