Novitates zoologicae : a journal of zoology in connection with the Tring Museum - British Museum (Natural History) (Zoological Museum, 1940)

Nuovi annali delle scienze naturali (1838)

Nuovi annali delle scienze naturali (1840)

Nuovi annali delle scienze naturali (1852)

Occasional papers - Boston Society of Natural History. (1904)

Occasional papers - Texas Tech University. Museum, (The Museum, 1988)

Occasional papers of the Boston Society of Natural History - Boston Society of Natural History. (Boston Society of Natural History, 1921)

Occasional papers of the Boston Society of Natural History - Boston Society of Natural History. (Boston Society of Natural History, 1904)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 1928)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 1970)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 1973)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 1974)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 1984)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 2010)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 2012)

Occasional papers of the California Academy of Sciences - California Academy of Sciences (California Academy of Sciences, 2013)

Occasional papers of the Museum of Natural History, the University of Kansas - University of Kansas. Museum of Natural History. (The University, 1975)

Occasional papers of the Museum of Natural History, the University of Kansas - University of Kansas. Museum of Natural History. (The University, 1976)

Occasional papers of the Museum of Natural History, the University of Kansas - University of Kansas. Museum of Natural History. (The University, 1985)

Occasional papers of the Museum of Zoology, University of Michigan - University of Michigan. Museum of Zoology. (University of Michigan, 1917)

Occasional papers of the Natural History Museum, the University of Kansas, Lawrence, Kansas - University of Kansas. Museum of Natural History. (The University, 1996)

Occasional papers of the San Diego Society of Natural History - San Diego Society of Natural History. (San Diego Society of Natural History, 1964)

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Ohio Biological Survey notes - Ohio Biological Survey. (Ohio Biological Survey, 2019)

Ohio fossils - La Rocque, Aurèle, 1909 -1990 (Ohio Dept. of Natural Resources, Division of Geological Survey, 1955)

On Atopophrynus, a recently described frog wrongly assigned to the Dendrobatidae - Myers, Charles W. (American Museum of Natural History, 1986)

On the reptiles and Batrachians of North America - Garman, Samuel, 1843 -1927 (Major, Johnston & Barrett, Yeoman, 1883)

On the structure and development of the skull in the Batrachia - Royal Society (Great Britain) (Royal Society, 1881)

On the type specimens of two Colombian poison frogs described by A.A. Berthold (1845), and their bearing on the locality "Provinz Popayan" - Berthold, Arnold Adolph, 1803 -1861 (American Museum of Natural History, 1996)

De ontwikkeling van het chondrocranium van Alytes obstetricans voor de metamorphose - Seters, Wouter Hendrik van. ("Het Klaverblad", 1921)

Opinions and declarations rendered by the International Commission on Zoological Nomenclature - International Commission on Zoological Nomenclature (Printed by order of the International Trust for Zoological Nomenclature, 1958)

O.S.U. naturalist - Ohio State University. Biological Club. (Biological Club of Ohio State University, 1901)

Our country's animals and how to know them. A guide to the mammals, reptiles and amphibians of Great Britain - Gordon, W. J. (Simpkin, Marshall, Hamilton, Kent, 1904)

Our living resources : a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems - United States. National Biological Service. (U.S. Dept. of the Interior, National Biological Service, 1995)

Outlines of economic zoölogy - Reese, A. M. (Albert Moore), 1872 -1965 (P. Blakiston's Son & Co, 1919)

Outlines of zoology - Thomson, J. Arthur (John Arthur), 1861 -1933 (Humphrey Milford, Oxford University Press, 1929)

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Pacific science - University of Hawaii. (University Press of Hawaii, 1950)

Palaeontology - Palaeontological Association (Palaeontological Association, 1990)

Palaeontology - Palaeontological Association (Palaeontological Association, 1998)

Paleocene amphibians from Cernay, France - Estes, Richard (American Museum of Natural History, 1967)

Pamietnik Fizyjograficzny (Druk K. Kowalewskiego, 1882)

Pamietnik Fizyjograficzny (Druk K. Kowalewskiego, 1918)

Panamá : puente biológico : las Charlas Smithsonian del Mes, 1996-1999 - Heckadon Moreno, Stanley. (Instituto Smithsonian de Investigaciones Tropicales, 2001)

Parasitology (Cambridge University Press, 1922)

Partnerships for sustainable forest ecosystem management : fifth Mexico/U.S. biennial symposium : October 17-20, 1994, Guadalajara, Jalisco, Mexico - Rocky Mountain Forest; Range Experiment Station (Fort Collins, Colo.) (U.S. Dept. of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, 1995)

The Philippine journal of science - Philippines. National Science Development Board. (Bureau of Science, 1920)

Philosophical transactions of the Royal Society of London - Royal Society (Great Britain) (Royal Society of London, 1844)

Philosophical transactions of the Royal Society of London - Royal Society (Great Britain) (Royal Society of London, 1881)

The pictorial museum of animated nature ... - Knight, Charles, 1791 -1873 (C. Knight, 1844)

The pictorial museum of animated nature - Knight, Charles, 1791 -1873 (C. Cox, 1844)

Plant associations of region two : potential plant communities of Wyoming, South Dakota, Nebraska, Colorado, and Kansas - Johnston, Barry C. (USDA Forest Service, Rocky Mountain Region, 1987)

Pointing the way : the distribution and evolution of some characters of the finger muscles of frogs - Burton, Thomas C. (American Museum of Natural History, 1998)

Postilla - Peabody Museum of Natural History. (Peabody Museum of Natural History, 1960)