scutellidæ

from The Century Dictionary.

• noun A family of irregular or exocyclic sea-urchins, typified by the genus Scutella; the shield-urchins, with flat, discoidal shell, often perforated or fissured, and with ramified grooves on the under side. See Echinarachnius, Mellita, sand-dollar, and cuts under cake-urchin and Encope. Also called Mellitidæ.