Genus — Y R 0 C A . 
Nyroca Fleming, Philos. ZooL, Vol. II., p. 260, 1822 . . Type N. nyroca. 
Aythya Boie, Isis 1822, p. 564 . . . . . . . . Type N. nyroca. 
Also spelt — 
Aithyia Gloger, in Froriep’s Notizen, Vol. XVT., p. 279, 1827. 
Aethyia, id., ih. 
Aifhya Kaup, Skizz Entwick Gesch. Nat. Syst., p. 99, 1829. 
Athya Brandt, in Lehmann Reise nach Buchara, p. 329, 1852. 
Aythyia Bonaparte, Comptes Rendus Sci. (Paris), Vol. XLIII., p. 651, 1856. 
Aythia Salvador!, Cat. Birds Brit. Mus., Vol. XXVII., p. 334, 1895. 
Ilyonetta Heine, Nomencl. Mus. Hein. Orn., p. 347, 1890 . . Type N. nyroca. 
Anatine birds with comparatively short bills, long wings, short tail, short 
legs, long toes, the hind toe widely lobed. 
The hill is comparatively short, though longer than the head, compara- 
tively broad and deep. The culmen ridge is ill-defined, the nail being 
somewhat obsolete and a little overhanging. The depth at the base is 
rather more than half its length and is equal to its breadth. A coarse 
comb can be observed on the internal edges of the upper mandible with a 
corresponding coarse serration present on the edges of the under mandible. 
The rami enclose a triangular unfeathered tract, the nail being not well 
marked off. The neck is short. 
The wings are long, the first primary longest and narrow, showing flight 
capabihty. 
The tail is short and square, about one-fourth the length of the wing, 
the feathers pointed to some extent. 
The legs are short and stout, the metatarsus showing the usual solitary 
row of scutes on the anterior portion ; in length it is just exceeded by the 
chord of the culmen. 
The toes are long, the middle toe equalling the tail in length and much 
exceeding the metatarsus ; the hind toe is long with a prominent broad lobe. 
This is the sole Australian representative of the large section of Ducks, 
known as Diving Ducks from their manner of feeding. 
It so closely resembles the northern species that I at one time only gave 
it subspecific rank ; its northern origin is therefore obvious, as a close ally 
occurs in the East Indies. 
Yet in New Zealand a “ Diving Duck ” lives which is in no way related 
to the Australian species, but is referred to a different genus, and that genus 
is unrepresented otherwise in the Southern Hemisphere. This constitutes 
another of the Austral-Neozelanic anomalies in this Order. 
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