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Show 1885.] DR. H. GADOW ON THE SPECIES OF RHEA. 321 (Villa Bella and Cuyaba) through Paraguay across the Parana into Uruguay. Its headquarters appear to be the pampas of Argentina, whence it extends southwards to the Rio Negro of Patagonia. Rh. darwini seems to be restricted to the eastern half of Patagonia and to South-eastern Argentina; about the Rio Negro of Patagonia both species occur together. Rh. macrorhyncha has been found in the Provinces ofPernambuco and Bahia. Its north-westward and westward range is probably limited not by the Amazons and its enormous tributaries, but by the broad thick belt of forest of the Amazonian subregion. Its occurrence in Guiana is therefore improbable. As Rh. americana does not seem to occur in the South-eastern provinces of Brazil, "probably the barrier between the two species is a continuously wooded country [and I should add the numerous low but rough mountain-ranges] between that district and the Sertoes de Bahia" (Forbes). Summary. The chief differences between the three species are the following :- Number of cervical vertebras Neck Hand Hind limb Toes Bill Skull Metatarsus Ambiens muscle ... Rhea americana. Rh. macrorhyncha. 15 long shorter shortest broad 16 long shortest shorter longer longest bill narrow with transverse scutes through its typically developed length. Rh. darwini. 15. short. longest. longer. longest. shortest bill. broad. scutes on distal half only. apparently sub-ject to fre-quent modifications. Tracheal rings greatest number smallest number. General coloration of plumage generally darker most of the fea-than Rh. amcri- thers with cana, especially white tips. on the head. Habitat Southern half of North-eastern South-eastern South America. Brazil. South America. This tabular arrangement shows that Darwin's Rhea differs considerably from the other two species, whilst the latter offer apparently few important characters for separation. However, no matter if the number of the neck-vertebrae of Rh. macrorhyncha (the best name for which would be that of the long-necked or slender-headed Rhea) be a constant character or not, the differences in the proportions of the skulls afford an anatomical character just as good as those which induce us to consider Rh. darwini a so-called good species. If we thus consider the three forms of Rhea as three equivalent |