Phytology. The department of Natural History which relates to plants. Botany.
Placoid. A group of fishes, so called from the structure of their scales.
Planorbis. A fresh water univalve. Fossil and recent.
Platygnathus. (Greek; platus, wide, and gnathos, jaw or mouth.)
Plesiosaurus. An extinct genus of reptiles.
Pliocene, Older and Newer. The upper part of the Tertiary series, so called by Sir C. Lyell from the preponderance of recent shells in them.
Plumbago (Black lead). The name commonly given to graphite, a form of carbon.
Plutonic rocks. Rocks supposed to be due to igneous action at great depths below the earth’s surface, have been thus named by older geologists. The igneous action is not manifest in such rocks, but presumed, as in the case of granite.
Polyparia. A group of animals of which the coral animal is a well known example.
Porcellia. The papaw, a plant now called asimina.