4. HYDROPEOGNE. 36 



Sylochelidon schillingi, Brehm, Viig. Deutachl. p, 770 (1831) ; id. 



Vonelf. p. 346 (1855) ; id. Naum. 1855, p. 295. 

 Helopus caspius, Wagl. Isis, 1832, p. 1224. 

 Thalassites melanotis, Sw. B. W. Afr. ii. p. 253 (1837) *. 

 Thalassites, n. sp. ?, no. 405, Jerdon, Madr. Journ. xii. p. 225 (1840). 

 Sylochelidon melauotis, Boie, Isis, 1844, p. 186 ; Bt). C. Ii. xlii. 



"p. 772(1856). 

 Sylochelidon macrorhjniclia, Boie, Isis, 1844, p. 186. 

 Sylochelidon strenuus, Gould, P. Z. S. 1846, p. 21 (Bass Straits and 



Tasmania, breeds) ; id. B. Austr. vii. pi. 22 (1848) ; Reichetih. 



Vof/. Neuholl. ii. p. 9 & p. 346 (18o0). 

 Sterna cayana, Richards. Journ. Boat-Voy. i. p. 87 & p. 155 (1851 : 



Great Slave Lake, breeds). 

 Sylochelidon strenua, Bp. C. R. xlii. p. 772 (1856). 

 Sterna melanotis, Hartl. Orn. West- Afr. p. 254 (1857) ; W. A. 



Forbes, Ibis, 1883, p. 500 (Bonny, large colony). 

 Sylochelidon caspica, Reichenb. Si/st. Nat. tab. iv. (1850), and 



Loncjipennes, p. 5 (1852). 

 Sterna major, Ellman, Zool. s. s. p. 7472 (1861 : New Zealand). 

 Thalasseus iinperator, Coues, Fr. Fhilad. Acad. 1862, p. 538 



(Labrador). 

 Sterna caspia, var. imperator, Ridgxo. Ann. Lye. N, Y, x. p. 391 



(1874). 

 Sterna (Thalasseus) caspia, Coues, B. N.- West, p. 667 (1874) ; id. 



Key N. Anier. B. 2nd ed. p. 757 (1884). 

 Thalas.seus caspicus, Rochebr. Faun. Seneg., Ois. p. 336 (1884). 



Adult male in breeding-plumage. Forehead, upper part of lores, 

 crown, and nape glossy greenish black; mantle pale french-grey ; 

 primaries the same -when new and frosted, but afterwards darker 

 grey, turning to slate-colour on the margins of the inner webs; 

 shafts white ; the usual paler " wedges" in the middle of the inner 

 webs hardly perceptible ; tail greyish white to white ; entire under- 

 parts pure white : bill vermilion-red, sometimes horn-coloured at 

 tip ; tarsi and toes black. Total length averages 20 inches, culmen 

 3-3, wing 16-5, tail G, depth of fork 1-25, tarsus 1-65, middle toe 

 with claw 1-7. There is considerable individual variation in 

 dimensions, quite irrespective of locality. 



Female. Similar, but shghtly smaller, with a weaker and less 

 brilliantly coloured bill. 



Adult in winter. Crown, nape, and lores streaked with white and 

 black, the latter colour thickest about the eyes and ear-coverts ; bill 

 orange-red, horn-coloured at the tip ; otherwise as in summer. 



Immature. Like the above, but orbital patch blacker; wing- 

 coverts, secondaries, and tail-feathers with a good deal of brownish 

 grey ; primaries ash-grey to dull brown towards the tips. 



Young. Similar, but feathers of the mantle and tail mottled 

 and barred with brownish black. 



Nestling, one dag old. Above pale buff, inconspicuously mottled 

 with dull brown, underparts dull white. Older nestlings show a 

 greyer tint above. 



Hah. Europe from about 60° N. lat. southwards : Asia to China 

 (not in Japan) ; Malayasia, Australia, New Zealand ; Africa ; 



* Type in Cambridge Museum examined. 



d2 



