Oologia neerlandica : eggs of birds breeding in the Netherlands - Lechner, Arnold Anthon van Pelt (Nijhoff, 1911)

Ootheca Wolleyana: an illustrated catalogue of the collection of birds' eggs - Newton, Alfred, 1829 -1907 (sold by R. H. Porter, 1902)

Opera ornithologica - Bonaparte, Charles-Lucien, 1803 -1857 (1857)

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)

Opuscula ornithologica : notis et addendis, mss - Coues, Elliott, 1842 -1899 (1861)

Orchid album :comprising coloured figures and descriptions of new, rare and beautiful orchidaceous plants (B. S. Williams, 1888)

Orchid album :comprising coloured figures and descriptions of new, rare and beautiful orchidaceous plants (B. S. Williams, 1891)

Orchid album :comprising coloured figures and descriptions of new, rare and beautiful orchidaceous plants (B. S. Williams, 1893)

The orchid-grower's manual, containing descriptions of the best species and varieties of orchidaceous plants in cultivation ... - Williams, Benjamin Samuel, 1822 -1890 (Victoria and Paradise nurseries, 1894)

The orchid hybrids Second supplement - Hansen, Geo. (George), 1863 -1908 (Geo. Hansen, 1897)

The Orchid review (Orchid Review ltd.], 1893)

The Orchid review (Orchid Review ltd.], 1894)

The Orchid review (Orchid Review ltd.], 1896)

The Orchid review (Orchid Review ltd.], 1897)

The Orchid review (Orchid Review ltd.], 1898)

The Orchid review (Orchid Review ltd.], 1899)

The Orchid review (Orchid Review ltd.], 1901)

The Orchid review (Orchid Review ltd.], 1907)

Organic evolution as the result of the inheritance of acquired characters according to the laws of organic growth - Eimer, Theodor, 1843 -1898 (Macmillan, 1890)

L'Organisation du Règne animal Oiseaux - Blanchard, Emile, 1819 -1900 (Chez l'Auteur)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1885)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1886)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1887)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1888)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1889)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1890)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1891)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1895)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1896)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1898)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1899)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1901)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1904)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1903)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1910)

Ornis - International Ornithological Committee. (Carl Gerold's Sohn, 1905)