The whole structure of this species is much more slender and _Certhia_-like than any other member of its genus, and I observed that this difference of form has a corresponding influence over its habits, which are more strictly arboreal than those of its congeners; indeed so much so, that it is questionable whether the bird ever descends to the ground. It also differs from the _C. scandens_ in the character of country and kind of trees it inhabits, being rarely seen on the large _Eucalypti_ in the open forest lands, but resorting to trees bordering creeks, as well as those on the mountains and the brushes. I have frequently seen it in the brushes of Illawarra and Maitland, in which localities the _C. scandens_ is seldom if ever found. While traversing the trunks of trees in search of insects, which it does with great facility, it utters a shrill piping cry: in this cry, and indeed in the whole of its actions, it strikingly reminded me of the Common Creeper of Europe (_Certhia familiaris_), particularly in its manner of ascending the upright trunks of the trees, commencing at the bottom and gradually creeping up the bole to the top, and generally in a spiral direction. It is so partial to the _Casuarinæ_, that I have seldom seen a group of these trees without at the same time observing the White-throated Tree-Creeper, the rough bark affording numerous receptacles for various kinds of insects, which constitute its sole diet. I have never seen this species near the water-holes, and I feel assured it has the power of subsisting without drinking. The breeding-season is in September and the three following months. The nest is built of grasses, is warmly lined with feathers, and is placed in the hollow branch or hole of a tree. The eggs are three in number, of a dull white thinly speckled with fine spots of rich brown, and a few larger blotches of the same colour; they are ten lines long by eight lines broad. Crown of the head and back of the neck sooty black; back olive-brown; wings dark brown, all the primaries and secondaries crossed in the centre by a dull buff-coloured band; throat and centre of the abdomen white, the latter tinged with buff; feathers of the flanks brownish black, with a broad stripe of dull white down the centre; rump and upper tail-coverts dark grey; under tail-coverts white, crossed by several bands of black, each of which being separated on the stem appear like a double spot; tail greyish brown, crossed by a broad band of black near the tip; bill black; the under mandible horn-colour at the base; feet blackish brown. The female is precisely the same in colour, with the exception of having a small orange-coloured spot just below the ear-coverts, and by which she is at once distinguished from her mate. The figures are those of a male and female of the natural size. [Illustration: ORTHONYX SPINICAUDUS: _Temm._ _J. Gould and H. C. Richter del et lith._ _Hullmandel & Walton Imp._ ]