588 MR. H. O. FORBES ON BIRDS FROM [DcC. 4, 



not make an ordinary web ; but only the thinnest film on the surface 

 of the leaf. The appearance of the excreta rather recently left by a 

 bird on a leaf is well known. There is a pure white deposit in the 

 centre, thinning out round the margin, while in the central mass are 

 dark portions variously disposed ; as the leaf is rarely horizontal, the 

 more liquid portions run for some distance. Now this Spider one 

 might almost imagine to have in its rambles 'marked and inwardly 

 discerned " what it had observed, and had set about practising tJie 

 " wrinkles " gained ; for it first weaves a small irregular patch of 

 white web on some prominent leaf, then a narrow streak laid down 

 towards its sloping margin ending in a small knob ; it then takes 

 its place on the centre of the irregular spot on its back, crosses its 

 black-angled legs over its thorax, and waits. Its pure white abdomen 

 represents the central mass of the bird's excreta, the black legs 

 the dark portions of the slime, while the web above described which 

 it has spun represents the more watery marginal part (become dry), 

 even to the run- off portion with the thickened knob (which was not 

 accidental, as it occurred in both cases), like the residue which semi- 

 fluid substances ending in a drop leave on evaporation. It keeps 

 itself in position on its back by thrusting under the web below it 

 the spines with which the anterior upper surfaces of the legs are 

 furnished. 



The most interesting fact of all to me is, not so much that of the 

 Spider having gained, which it can, of course, have no consciousness 

 of, by natural selection the colour and form of an excretum, but that it 

 has acquired the habit of supplementing its own colour and form by 

 an addition in such absolute harmony with that of which itself is the 

 similitude. 



4. On a new Species of Thrush from Timor Laut^ with 

 remarks on some rare Birds from that Island and from 

 the Moluccas. By H. O. Forbes, F.Z.S. 



[Received November 20, 1883.] 



(Plates LII. & LIII.) 



The specimen of Qeocichla which I have now the pleasure of exhi- 

 biting (Plate LII.) is an adult male of a species intermediate between 

 G. rubiginosa of Timor and G. erythronota of Celebes, two species 

 which are also now represented on the table through the kindness of 

 Mr. H. Seebohm. The general colour of the upper parts is olive-brown, 

 shading into slaty brown on the head and into chestnut on the rump 

 and upper tail-coverts; lores white, ear-coverts mottled white and slaty 

 brown; wings brown; lesser wing-coverts olive-brown, broadly tipped 

 with white; innermost secondaries russet-brown, obscurely tipped with 

 white ; tail-feathers russet-brown, the outer feathers on each side 

 broadly tipped with dull white ; chin, throat, and breast huffish 



