Having lately, in a re-examination of the Wealden fossil described in the Transactions of this Society, chiefly on my authority, as the tarso-metatarsal bone of a Bird, exposed by the detachment of the matrix that adhered to its extremity some characters not visible when the fossil was first submitted to me, and having been led by those new characters to institute a more extended and rigorous comparison of the fossil than it was in my power to do ten years ago, I believe myself in a condition to demonstrate my former error in ascribing it to the class of Birds, and I therefore lose no time in rectifying it. The character mainly relied on as proving the fossil in question to be the lower end of a tarso-metatarsal bone of a wading bird, was the rough oval spot marked o in fig. 1 b , pl. 13, of the above-cited volume, and this, if interpreted as the articular surface for the hind-toe, would indicate a form of metatarsal bone like that of the restored figure given by Dr. Mantell, by the dotted outline in the above-cited plate. But the characters since brought to light prove the bone (fig. 1) to have terminated much nearer the oval spot ( o ), since they consist of two portions of the distal smooth articular surface, one ( a , fig.1 & 3) situated near the margin of one side of the joint, at right angles to the axis of the bone; the other surface ( b ) being a smooth