IN the Anales of the Buenos Aires Museum for 1912 (vol. xii.) Sefior Cardoso adduced evidence to show that the story of the origin of Argentine horses from Spanish horses imported by Don Pedro de Mendoza m X535 or X536 is a myth, and that the former are really descended from the Pleistocene Equus rectidens and E. curilidens, and existed in the interior of the country at the time of the Spanish conquest. This opinion is disputed in the Revue genorale des Sciences of October 15 by Dr. Trouessart, who points out that the statement of wild horses having been seen by Sebastian Cabot in 1531 is based on the figure of a horse introduced by that navigator in a map of the world in the region now known as Argentina. This, it is urged, is no evidence at all, but merely an indication that the country was suitable for horses. Historical evidence is cited to prove that horses were unknown to the Indians of Mexico, Panama, Peru, and Brazil at the time of the visits of Columbus (1498 and 1502), and of the opening up of the country by his successors. It is then shown that there is a hiatus between the beds containing remains of E. rectidens and those with bones of modern horses, while it is argued that the ancient indigenous perisso-dactyles became extinct as the result of climatic and other physical changes. That the historical evidence in the case of the countries mentioned is decisive may be admitted, but the statements of Senor Cardoso with regard to the existence of large numbers of horses in Argentina in 1580 and the lack of fear of these animals exhibited by the Indians, as well as certain structural peculiarities alleged to be peculiar to Argentine horses and E. rectidens, are not referred to by Dr. Trouessart, who had not seen the original paper when writing his own article. A summary of Senor Cardoso's views will be found in The Field of July 20, 1912.