298 LARIDA. 
length. The pterylosis resembles that of the Snipes (Scolopacin), and the tail is 
more or less distinctly forked. | 
Eleven genera of Terns are recognized by Mr. Howard Saunders, and four of them 
are found in Central America. | 
HYDROCHELIDON. 
Hydrochelidon, Boie, Isis, 1822, p. 563 ; Saunders, Cat. Birds Brit. Mus. xxv. p. 5 (1896). 
This genus includes four species of small size, with a blackish under surface in 
summer, changing to white in winter, the young being also white below. ‘The tail is 
not very deeply forked, and is short, being less than half the length of the wing; the 
rectrices are rounded or slightly pointed. The bill is small, with the culmen less than 
twice the length of the tarsus: the feet are feeble, and the webs between the toes 
considerably indented (cf. Saunders, J. v.). 
Of the four species known, one is peculiar to the New World, and two of the 
Eastern forms, viz. H. leucoptera and H. hybrida, have occurred incidentally in 
American waters. 
1. Hydrochelidon surinamensis. 
Surinam Tern, Lath. Gen. Syn. iii. 2, p. 352. 
Sterna surinamensis, Gm. Syst. Nat. i. p. 604°. 
Hydrochelidon nigra surinamensis, Baird, Brewer, & Ridgway, Water-Birds N. Amer. iil. p. 318° ; 
Ferrari-Perez, Pr. U. S. Nat. Mus. ix. p. 179*; Zeledon, An. Mus. Nac. Costa Rica, 1887, 
p. 183°; A. O. U. Check-l. N. Amer. Birds, 2nd ed. p. 26°. 
Pelodes surinamensis, Heine & Reichenow, Nomencl. Mus. Hein. p. 356". 
Hydrochelidon surinamensis, Saunders, Cat. Birds Brit. Mus. xxv. p. 20°; Oates, Cat. Eggs Brit, 
Mus. i. p. 176, t. 18. fig. 5°. 
Sterna frenata, Scl. & Salv. Ibis, 1860, p. 278”. 
Hydrochelidon plumbea, Lawr. Ann. Lyc. N. Y. vii. p. 479"; Scl. P. Z. 8S. 1864, p. 179”; Scl. 
& Salv. P. Z. 8. 1864, p. 873°. 
Hydrochelidon fissipes, Salv. Ibis, 1864, p. 885™*; 1866, p. 205%; Coues, Ibis, 1864, p. 891”; 
Scl. & Salv. P. Z.S. 1871, p. 573°"; Lawr. Mem. Bost. Soc. N. H. ii. p. 318°; Bull. U.S. 
Nat. Mus. no. 4, p. 52°°; Sumichr. La Nat. v. p. 234°. 
Sterna superciliaris, Lawr. Mem. Bost. Soc. N. H. ii. p. 818 *!; Sumichr. La Nat. v. p. 2384”. 
Hydrochelidon lariformis, Streets, Bull. U. 8. Nat. Mus. vii. p. 27”. 
2. Ptil. estiv. Supra saturate schistacea, alis dorso concoloribus, remigibus nigricantibus, primariis extus et 
ad apicem cineraceis, rhachidibus albis, secundariis intimis omnino cineraceis; margine alari albo; cauda 
cineracea; pileo toto nigro, collo postico nigro adumbrato ; facie laterali et corpore subtus toto fumoso- 
nigris; tibiis, crisso et subcaudalibus albis; subalaribus albidis, majoribus, axillaribus et remigibus intus 
pallide cineraceis: rostro nigro ; pedibus saturate brunneis; iride saturate brunnea. Long. tota circa 9-0, 
ale 7:9, caude 2°8, culm. 1:25, tarsi 0°55. (Descr. feminze adulte ex Cay Dolores Channel. Mus. 
nostr.) 
3. Ptil. hiem. Supra cinerea; torque collari albo; pileo cineraceo, plumis medialiter nigris et cano adum- 
bratis ; fronte, loris, regione oculari, facie laterali et corpore subtus toto albis, regione anteoculari et 
