Plac"oid (?), a. [Gr. &?;, &?;, a tablet + -oid.] (Zoöl.) Platelike; having irregular, platelike, bony scales, often bearing spines; pertaining to the placoids.

Plac"oid, n. (Zoöl.) (a) Any fish having placoid scales, as the sharks. (b) One of the Placoides.