GELOCHELIDON.—HYDROPROGNE. 401 
as a lining. The eggs are generally three, rarely four, in number; they are of a 
broad oval shape, the ground-colour varying from a greyish- or buffish-white to a pale 
buff, stone-colour, or brown; the markings are of small size and evenly distributed 
over the shell, consisting of spots and blotches of dark brown or olive-brown, with very 
prominent underlying grey !°. 
HYDROPROGNE. 
Hydroprogne, Kaup, Natiirl. Syst. p. 91 (1829); Saunders, Cat. Birds Brit. Mus. xxv. p. 32 
(1896). 
The single species of the genus Hydroprogne is a bird of large dimensions, with a 
red bill of exceptional size, stoutness, and depth. Tail very short, being less than 
one-third of the wing; the outer tail-feathers are the longest and are pointed. Tarsus 
short, being less than the length of the middle toe and claw. H. caspia is found in 
nearly all temperate and tropical regions. 
1. Hydroprogne caspia. 
Sterna caspia, Pall. N. Comm. Petrop. xiv. 1, p. 582, t. 22. fig. 2'; Baird, Brewer, & Ridgway, 
Water-Birds N. Amer. ii. p. 280’. 
Hydroprogne caspia, Saunders, Cat. Birds Brit. Mus. xxv. p. 32°; Oates, Cat. Eggs Brit. Mus. i. 
p. 178°. 
Sterna ischegrava, A. O. U. Check-l. N. Amer. Birds, p. 23 °, 
Ptil. estiv. Maxima: supra delicate margaritaceo-cinerea ; rectricibus dorso concoloribus, intus et ad 
apicem albis; alis dorso concoloribus, secundariis intus albidioribus, primariis saturatioribus, intus vix 
nigricantibus, juxta rhachidem albam et pogonio externo schistaceis ; pileo nuchaque cum loris dimi- 
diatis et plumis subocularibus virescenti-nigerrimis ; macula suboculari alba; loris inferioribus, facie 
laterali et corpore subtus toto pure albis: rostro miniato, interdum apicem versus corneo; pedibus 
nigris ; iride saturate brunnea. Long. tota circa 20°0, ale 17-2, caude 4°2, rectrice extima 5°7, culm. 2°9, 
tarsi 1-6. (Descr. maris adulti ex Corpus Christi. Mus. nostr.) 
Ptil. hiem. Ptilosi estive similis, sed pileo nigro, albo maculato et linealiter striato. Long. tota circa 21-0, 
ale 16°0. (Descr. maris adulti ex Presidio. Mus. nostr.) 
Hab. Norra America, from a little beyond the Arctic Circle, breeding southward to 
Virginia, Lake Michigan, Texas, Nevada, and California ?°,—Mexico, Mazatlan, 
Presidio (Forrer *).—Evrore from about 60° N. lat. southwards; Asia to China ®; 
Matayasta to Australia and New Zealand?; AFRICA °. 
In Central America this bird can be scarcely more than a winter visitor, two 
specimens only having been procured near Mazatlan by Mr. Forrer, one in December 
and another in February °. 
It is chiefly an inhabitant of the sea-shores and adjacent islands, but is also found 
on inland seas and lakes. Its eggs, laid in a depression of the sand, are similar to 
those of the Gull-billed Tern, but larger *. 
BIOL, CENTR.-AMER., Aves, Vol. IIL., November 1903. 51 
