Ornithorhynchus. A singular animal, found in New Holland, called also the water-mole.
Orthocera. A straight-chambered shell of the Silurian formation.
Osseous. Bony: Osseous breccia is a conglomerate made up of bones cemented together by lime, and mixed with earthy matter.
Osteolepis (bone-scale). A fish of the Old red sandstone.
Osteological. Relating to bones.
Outcrop. The line at which a stratum first shows itself at the surface in inclined deposits.
Oviparous. Egg-laying animals.
Pachydermata. A group of animals so called from the thickness of their skin. The elephant and pig are well known examples.
Palæoniscus. A fossil fish of the Magnesian limestone of England.