Joseph Leidy, an American naturalist, born in Philadelphia, Sept. 9, 1823. In 1844 he graduated M. D. at the university of Pennsylvania, and began the practice of medicine; but he soon devoted himself to teaching, and to original work in the biological sciences. In 1846 he was chosen chairman of the curators of the national academy of sciences, and in 1853 professor of anatomy in the university of Pennsylvania, which chair he still fills (1874). In March, 1871, he was appointed professor of natural history in Swarthmore college, teaching zoology, comparative anatomy and physiology, mineralogy, and geology, without intermitting his duties in the university. During the civil war his scientific labors were to a great extent arrested by his services as acting assistant surgeon in Satterlee hospital, Philadelphia. His contributions to scientific periodicals number nearly 800. He has also written " Flora and Fauna within Living Animals," "Ancient Fauna of Nebraska," and "Cretaceous Reptiles of the United States" (published by the Smithsonian institution); "The Extinct Mammalian Fauna of Dakota and Nebraska, together with a Synopsis of the Mammalian Remains of North America" (4to, 30 plates, Philadelphia, 1870); and "Contributionsto the Extinct Vertebrate Fauna of the Western Territories" (4to, 37 plates, Washington, 1873).