PLEONASM

(Gr. ir\cov, more.) In Rhetoric, a re dundant phrase or expre ion, sometimes introduced to gtw additional energy, at other limes needle and ungraceful. PLESIOMO'hTlllSM. (Gr. irXnaios, near, and v„a$n form.) A term applied to crystallized substances the forms of which closely resemble each other, but arc not absolutely identical. The primary form of sulphate of strontia If ■ rhombic prism very similar to that of sulphate of baryta. but, on measuring the inclination of corresponding sides on each prism, the difference exceeds ii°. Similar differences are observable in the rhomboedrons of carbonate of lime and carbonate of iron. Such substances, therefore, arc plesiomnrphous. PLESIOSAUR, Plesiosaur us. (Gr. rXqcrio?, and onvpoc, a lizard.) The name of a genus of extinct marine saurians, chiefly remarkable for their length at neck. The head is small, but like that of a crocixlile; the vertebra; are articulated generally by nearly plane surfaces; the cervical vertebra1 have an articular surface, divided by a longitudinal impre ion, for a rudiments] rib on each side, and two m< cular foramina beneath the digital bones of both the hind and fore extremities are flattened, and are enveloped in a sheath of sKin like the paddles of the Cetacea. The remains of the Plesiosaur i occur in the formations from the muschel-chalk to the chalk inclusive; but are most common in the lias and kimmcridge clav beds. [s. 959]