Okens Lehrbuch der Naturgeschichte - Oken, Lorenz, 1779 -1851 (Bei Carl Heinrich Reclam, 1816)

Old bones : or, Notes for young naturalists, on vertbebrate animals, their fossil predecessors and allies - Symonds, W. S. 1818 -1887 (Robert Hardwicke, 1864)

The old forest ranger, or, Wild sports of India on the Neilgherry Hills, in the jungles and on the plains - Campbell, Walter. (How and Parsons, 1842)

The Oligocene Hsanda Gol Formation, Mongolia : a revised faunal list - Mellett, James Silvan, 1936 - (American Museum of Natural History, 1968)

Olivier's Entomologie oder Naturgeschichte der Insekten mit ihren Gattungs- und ArtMerkmalen, ihrer Beschreibung und Synonymie. Käfer - Sturm, Jakob, 1771 -1848 (Gedrukkt und im Verlage bei Karl Reichard, 1800)

Om rätta tydningen af sido-utskotten på rygg- och ländkotorna hos menniskan och däggdjuren - Retzius, A. (Anders), 1796 -1860 (Norstedt, 1850)

On certain phenomena belonging to the close of the last geological period and on their bearing upon the tradition of the Flood - Prestwich, Joseph, Sir, 1812 -1896 (Macmillan, 1895)

On the anatomy of vertebrates - Owen, Richard, 1804 -1892 (Longmans, Green, 1866)

On the anatomy of vertebrates ... - Owen, Richard, 1804 -1892 (Longmans, Green and Co, 1866)

On the classification and geographical distribution of the Mammalia, being a lecture on Sir Robert Reade's foundation, delivered before the University of Cambridge ... May 10, 1859. To which is added an appendix "On the gorilla," and "On the extinction and transmutation of species." - Owen, Richard, 1804 -1892 (J. W. Parker and son, 1859)

On the flat-clawed carnivora of the eocene of Wyoming - Cope, E. D. (Edward Drinker), 1840 -1897 (American Philosophical Society, 1873)

On the geology and natural history of the upper Missouri :Being the substance of a report made to Lieut. G.K. Warren, T.E. U.S.A - Hayden, F. V. (Ferdinand Vandeveer), 1829 -1887 (Printed by C. Sherman & son, 1862)

On the habits and instincts of animals - Swainson, William, 1789 -1855 (Printed for Longman, Orme, Brown, Green, & Longmans, 1840)

On the plains, and among the peaks, or, How Mrs. Maxwell made her natural history collection - Ridgway, Robert, 1850 -1929 (Claxton, Remsen & Haffelfinger, 1879)

On the power, wisdom, and goodness of God : as manifested in the creation of animals, and in their history, habits, and instincts - Jones, Thomas Rymer, 1810 -1880 (H.G. Bohn, 1853)

On the power, wisdom and goodness of God, as manifested in the creation of animals, and in their history, habits and instincts - Kirby, William, 1759 -1850 (Carey, Lea & Blanchard, 1836)

On the power, wisdom and goodness of God as manifested in the creation of animals and in their history, habits and instincts - Kirby, William, 1759 -1850 (W. Pickering, 1835)

On the zoology of ancient Europe; a paper read before the Cambridge Philosophical Society, on Monday, 31st March, 1862 - Newton, Alfred, 1829 -1907 (Macmillan, 1862)

The Ontario natural science bulletin - Wellington Field Naturalists' Club. (Wellington Field Naturalists' Club, 1905)

The Ontario natural science bulletin - Wellington Field Naturalists' Club. (Wellington Field Naturalists' Club, 1912)

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, 1944)

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, 1947)

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)

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, 1955)

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, 1956)

Opuscoli scientifici d'entomologia, di fisica e d'agricoltura - Termeyer, Ramón María, 1737 -1814 (Nella Stamperia del Giornale italico di Carlo Dova, contrada S. Rafaello, num. 998, 1807)

The Orchid world. A monthly illustrated journal entirely devoted to orchidology - Wilson, Gurney, 1878 - (Alabaster, Passmore & Sons, ltd., printers], 1913)

The orders of mammals - Gregory, William K. (William King), 1876 -1970 (The Trustees, 1910)

Organic remains of a former world. An examination of the mineralized remains of the vegetables and animals of the antediluvian world; generally termed extraneous fossils - Parkinson, James, 1755 -1824 (Sherwood, Neely and Jones, etc, 1811)

The origin and relationship of the large mammals of North America - Grant, Madison. (Reprinted from the eighth annual report of the New York Zoological Society, 1904)

The origin and relationship of the large mammals of North America - New York Zoological Society. (1904)

The origin of the fittest : essays on evolution - Cope, E. D. (Edward Drinker), 1840 -1897 (D. Appleton, 1887)

The origin of the fittest : essays on evolution - Cope, E. D. (Edward Drinker), 1840 -1897 (Macmillan and Company, 1887)

The origin of the fittest; essays on evolution - Cope, E. D. (Edward Drinker), 1840 -1897 (D. Appleton, 1887)

L'origine et le développement des flores dans le massif central de France; avec aperçu sur les migrations des flores dans l'Europe sud-occidentale - Braun-Blanquet, J. (Josias), 1884 -1980 (L. Lhomme, 1923)

Ornithological journal and register - Mearns, Edgar Alexander, 1856 -1916 (1874)

Ornithologische Monatsschrift - Deutscher Verein zum Schutze der Vogelwelt. (Kommissions-Verlag der Creutschen Verlagsbuchhandlung, 1903)

Ornithology - Jardine, William, 1800 -1874 (W.H. Lizars, 1853)

Ostéographie, ou, Description iconographique comparée du squelette et du système dentaire des Mammifères récents et fossiles : pour servir de base à la zoologie et à la géologie - Blainville, H.-M. Ducrotay de (Henri-Marie Ducrotay), 1777 -1850 (J.B. Baillière et fils, 1839)