LEIDY, Joseph, naturalist, born in Philadelphia, Pennsylvania, 9 September, 1823. He early acquired a knowledge of mineralogy and botany by his own efforts, studied medicine under Dr. Paul B. Goddard. and was graduated in that department at the University of Pennsylvania in 1844. At first he became assistant in the chemical laboratory of Robert Hare and James B. Rogers, also practising medicine, but in 1846 he wholly relinquished the practice of his profession, excepting during the civil war, when he entered the United States volunteer army and served as a contract surgeon in the Satterlee general hospital in Philadelphia, Pennsylvania Meanwhile, in 1845, he became prosector to the chair of anatomy in the University of Pennsylvania, which was then held by Dr. William E. Homer, and in 1846 became demonstrator of anatomy in Franklin medical college. The latter appointment he held for one session only, and then he renewed his association with Dr. Horner, with whom he also gave a private course of anatomical lectures. He visited Europe in 1848, examining the museums and hospitals there, and on his return lectured on microscopic anatomy, and in 1849 begun a course of lectures on physiology at the Medical institute. In 1852 he took Dr. Horner's place, and delivered his lectures to the completion of the course, and on the death of the latter in the following year Dr. Leidy was elected to the chair of anatomy. In 1871 he was also called to the Chair of natural history in Swarthmore college, and he still (1887) holds both these posts. Professor Leidy, in 1884, on the establishment of the department of biology in the University of Pennsylvania, became its director, which office he still fills. He is an accomplished draughtsman, and in 1844, when Dr. Amos Binney was about to publish his work on the terrestrial air-breathing mollusks, he selected Professor Leidy to dissect and draw the internal organs of the species that were to be described. Professor Leidy obtained the Walker prize of $1,000 from the Boston society of natural history in 1880, and also the Lvell medal with the stun of £25 from the Geological society of London "in recognition of his valuable contributions to paleontology," and received in 1886 the degree of LL. D. from Harvard. He is a member of numerous scientific societies, in 1884 was elected to the National academy of sciences, and is president of the Philadelphia academy of natural sciences. The titles of his published papers exceed 800 in number, all on biological subjects, of which many are from specimens obtained on the various surveys under the United States government and submitted to him for study and report. His first paleontological paper, published in 1847, was "On the Fossil Horse," a subject which later, in the hands of Thomas H. Huxley and Othniel C. Marsh, has been used in the illustration of the theory of evolution. Professor Leidy's principal works are " Memoir on the Extinct Species of American Ox" (1852); "A Flora and Fauna within Living Animals" (1853); "Ancleat Fauna of Nebraska" (1853), "On the Extinct Sloth Tribe of North America" (1855); "Cretaceous Reptiles of the United States" (1865); "The Extinct Mammalian Fauna of Dakota and Nebraska" (1869); "Contributions to the Extinct Vertebrate Fauna of the Western Territories" (1873); "Description of Vertebrate Remains from the Phosphate Beds of South Carolina" (1877); "Fresh Water Rhizopods of North America" (1879); "The Parasites of the Termites" (1881); "On Manayunkia speciosa" (1883); and "Tape Worm in Birds" (1887). The foregoing have been issued by the Philadelphia academy of natural sciences, the Smithsonian institute, and under the auspices of the National government. He is also the author of "An Elementary Text Book on Human Anatomy" (Philadelphia, 1861).