BIEDS OF NORTH AND. MIDDLE AMERICA. 527 



KEY TO THE SPECIES AND SUBSPECIES OF HYDUOCHELIDON. 



a. Under parts not white; pileum uniform black. (Summer adults.) 



b. Upper tail-coverts and lower rump gray, concolor with bark, etc.; smaller 



wing-coverts not conspicuously paler than back. 



c. Sides of head white; under parts pale gray anteriorly, becoming much darker 



gray on flanks and abdomen; larger (wing 213.5-249, tarsus 19-22). (Southern 

 and central Europe to China, Philippines, Australia, Africa, etc.; accidental 



in Barbados.) Hydrochelldon leucopareia (p. 528). 



cc. Whole head, nock, and under parts (except anal region and under tail- 

 coverts) uniform black or deep gray; smaller (wing 191-215. tarsus 14-18). 

 • {Hydrochelldon nigra . ) 

 d. Under parts gray (Light purplish gray to blackish purple-gray). (Europe 

 and western Asia; Africa in ^vinter.') 



Hydrochelldon nigra nigra (^extralimital).^ 

 dd. Under parts black. (North America, south in winter as far as Chile.) 



Hydrochelldon nigra surinapiensis (p. 532). 



hb. Rump white, in contrast with dark gray or grayish black c4 back; smaller 



wing-coverts conspicuously paler than back, passing into white anteriorly. 



(Warmer parts of Eastern Hemisphere; accidental in Wisconsin and Barbados.) 



Hydrochelidon leucoptera (p. 536). 

 aa. Under parts white; pileum not uniform black. 



6. Back, scapulars, etc., uniform gray. (Winter adults.) 

 c. Rump gray, concolor with back, etc. 



d. Larger (wing 213.5-249, tarsus 19-22;; upper parts much paler gray; bill 



brownish Hydrochelidon leucopareia, winter adults (p. 528) . 



dd. Smaller (wing 191-215, tarsus 14-18); upper parts much darker gray; bill 



black Hydrochelidon nigra nigra, winter adults (extralimital). 



Hydrochelidon nigra surinamensis, winter adults (p. 533). 

 cc. Rump white Hydrochelidon leucoptera, winter adults (p. 537). 



a[Stema] nigra Linnaeus, Syst. Nat., ed. 10, i, 1758, 137 (Sweden).— Sterna nigra 

 Selby, Brit. Birds, ii, 1833, 477, pi. 91;Gould, Birds Europe, v, 1837, pi. 422; Nau- 

 mann, Vog. Deutschl., x, 1840, 189, pi. 256. — Hydrochelidon nigra Boie, Isis, 1822. 563; 

 Macgillivray, Brit. Birds, v, 1852, 658; Gould, Birds Great Brit., v, 1873, pi. 75 and 

 text; Dresser, Birds Europe, viii, 1876, 327, pi. 592; Saunders, Proc. Zool. Soc. Lond., 

 1876, 642 (monogr.); Cat. Birds Brit. Mus., xxv, 1896, 17; ed. Yarrell's Hist. Brit. 

 Birds, iii, 1884, 516; Man. Brit. Birds, 1889, 617 .--Hydrochelidon nigra nigra American 

 Oniithologists' Union, Check List, 3d ed., 1910, 47. — Viralva nigra Stephens, Shaw's 

 Gen. Zool., xiii, pt. i, 1826, 167.^ — Hydrochelidon nigrum Bonaparte, Geog. and Comp. 

 List, 1838, 6i.—[Rallus] larif ormis Linnssus, Syst. Nat., ed. 10, i, 1758, 153(Europei.— 

 [Hydrochelidon lariformis.] a. (Eiu^opean references) Coues, Birds Northwest, 1874, 

 704..— [Sterna] nxvia Linnaeus, Syst. Nat., ed. 12, i, 1766, 228 (south E urope= young). — 

 Larus merulinus Scopoli, Ann. L Hist. Nat., 1769, 81.— (?)Larus colunibinus Scopoli, 

 Ann. I. Hist. Nat., 1769, SS.— Sterna nubilosa Sparrman, Mus. Carls., fasc. iii, 1788, 

 no. 63 (Finland ;=young). — Sterna fissi pes (not of Linnaeus) Latham, Index Orn., ii, 

 1790, 810; Bechstein, Naturg. Deutschl., ii, 1791, 833; Yarrell, Brit. Birds, iii, 1843. 

 413; ed. 2, iii, 1845, 523; Schlegel, Mus. Pays-Bas, vi, Sternae, 1863, 29; Harting, Handb, 

 Brit. Birds, 1872, 76.— Hydrochelidon fissipes Bonaparte, Cat. Ucc. Eur., 1842, 77; 

 Degland and Gerbe, Orn. Eur., ii, 1867, 465; Fritsch, Vog. Eur., 1870, 462, pi. 54, 

 fig. 6; Salvadori, Fauna Ital., Ucc, 1871, 284.— Hydrochelidon obscura Brehm, Vog. 

 Deutschl., 1831, 795. — Hydrochelidon nigricans Brehm, Vog. Deutschl., 1831, 795. — 

 Hydrochelidon pallida Brehm, Naumannia, 1855, 295; Vogelf., 1855, 350. — Hydro- 

 chelidon obscura Brehm, Naumannia, 1855, 295; Vogelf., 1855, 350. 



