112 
garded as identically the same, because no external difference is per- 
ceptible, breed at opposite seasons in the two hemispheres, and that 
if the birds of one hemisphere be brought and retained in the other, 
they continue to moult their feathers and to breed at the same period 
that they would have done had they remained in their native country. 
567. Sternula Nereis, Gould Yol. VII. PI. 29. 
Genus Gelochelidon. 
It would be strange if this form did not exist in Australia, when 
all the other European genera of Terns are found there ; still I have 
no other evidence of such being the case, than that of a specimen 
in the collection of King’s College, London, which is said to be from 
Van Diemen’s Land, and to which in the year 1837 I gave the name 
of Sterna macrotarsa. 
ft 
568. Gelochelidon macrotarsus, Gould. 
Sterna macrotarsa , Gould in Proc. of Zool. Soc., Part V. p. 26 ; 
and in Syn. Birds of Australia, Part If. 
Crown of the head and back of the neck black; all the upper 
surface and primaries light silvery-grey ; remainder of the plumage 
white ; bill and feet black. 
As I did not meet with this bird myself either in Van Diemen’s 
Land or in any other of the Australian regions, I have not figured it. 
Genus Gygis. 
One species of this Polynesian genus of Terns is found in 
Australia. 
569. Gygis Candida Vol. VII. PI. 30. 
Genus Hydrochelidon. 
The value of minor genera or subgenera, as naturalists may choose 
to designate them, is much strengthened, when species, which have 
been assigned to either of them from countries so distant from each 
other as Australia and Europe, are found to possess similar habits, 
but differing from those of the other members of the family. Thus 
the members of the present little group inhabit the inland waters and 
marshes of both countries; make their nests among the rushes, and 
lay thickly-marked eggs, in both of which particulars they differ 
from the other Terns ; the generality of which deposit their eggs on 
the shingles of the sea-shore, while others, the Gygis Candida for 
instance, lay their single egg on the horizontal branch of a tree, so 
totally unprotected, that how it is retained in its position during 
windy weather is a perfect mystery ; others again, such as the Nod- 
dies, bring together large masses of sea-weed, which they either pile 
upon the swinging branch of a Mangrove or on the jutting point of 
a rock. All these facts should be studied by ornithologists before they 
discard subgenera proposed by their fellow labourers, and replace 
the species they may have so divided in the genera of the older 
writers, who must necessarily have known less of the subject ; for 
