The second species, to which the name of _Rhea Darwinii_ has been applied by Mr. Gould, takes the place of the former species—Rhea Americana, in Southern Patagonia, the part about Rio Negro being neutral ground. The first notice Mr. Darwin had of this species was in accidentally hearing the Guachos talking of a very rare bird, the Avestruz Petise; afterward, when among the Patagonian Indians in the Straits of Magellan, Mr. Darwin found a half-bred Indian who had lived some years with this tribe, but had been born in the Northern Provinces. On being asked if he had ever heard of the Avestruz Petise, he answered by saying, “Why there are none others in these Southern Countries;” and afterward many of these birds were seen; their distinctive characters being that they are light brown, in place of gray, and the bird altogether smaller than the Rhea Americana. In the year of grace, 1839, there was brought from New Zealand, by Mr. Rule, a most hopeless-looking osseous fragment, just the middle of a thigh-bone, without a scrap of either end remaining. This, which most persons would have regarded with despair, was placed in the hands of the great authority in such matters, with a request that he would state to what creature it had belonged. After a careful examination, Professor Owen, in a paper read before the Zoological Society, on the 12th of November, 1839, (and which paper is one of the most remarkable examples of acute inductive reasoning ever published,) announced that, “So far as my skill in interpreting an osseous fragment may be credited, I am willing to risk the reputation for it on the statement that there has existed, if there does not now exist, in New Zealand, a Struthious bird, nearly, if not quite equal in size to the ostrich.”