THE ISLANDS OF THE BAT OF BENGAL. 317 



I have heard them utter is a low "whistle, and this apparently- 

 only at night when they are feeding." 



975 Us.— Prion, Sp. ? (0.) 



When at sea, between Preparis and the Cocos on the 4th of 

 March, we saw several parties of blue and white petrels ; the 

 officers of the ship called them whale birds, but they were 

 manifest Prions of some species or others. 



976 — Thalassidroma, Sp. ? (0.) 



The same day, some hours earlier, we saw a few, small 

 dusky petrels, of the stormy petrel type, hovering about a 

 mass of water-logged cocoanut stems and other wood. We 

 changed the course of the steamer two or three times and even 

 lowered a boat, but we failed to get anywhere near any of 

 them. 



989 Us.— Sterna gracilis, Gould. (3.) 



It is with considerable doubt that I refer to this species, 

 three specimens of a beautiful little tern killed at the Anda- 

 mans during July last, I having no specimens of that species 

 to refer to, and neither Gould's description in the Hand-book 

 of the Birds of Australia, (and he gives no dimensions), 

 nor Professors Schlegei's brief diagnosis in the " Musee, Pays 

 Bas," sufficing to enable me to make certain of the species. 

 Indeed these birds appear to me in some respects intermediate 

 between gracilis, Gould, and paradisea, Briiun. 



The total length of the bird is about 14 inches ; wing, 8*5 ; 

 tail which extends an inch beyond the points of the wings, 

 nearly 7 ; the bill, which is very slender, is in shape almost 

 a perfect counterpart of that of Sternula melanauchen, and 

 measures 1*4 to 1*5 from forehead to point. The tarsus is 

 0*75; mid toe and claw, 09; the webs are ample, scarcely at 

 all scalloped. 



The bill was orange red ; the legs and feet red, claws brown ; 

 the entire top and back of the head, and a point descending 

 on the nape, velvet black, the black extends on the sides o 

 the head in a straight line almost but not quite as low as the 

 lower margin of the eye. The whole of the side of the head 

 below this, the chin, throat, neck all round, breast and entire 

 lower parts, and the whole of the outer tail feathers, pure 

 white ; the white of the cheeks just extends up to the central 

 one-third of the lower margin of the eye. The rest of the 

 upper parts, except the first three primaries, very delicate pale 



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