echinidæ

from The Century Dictionary.

• A family of regular desmostichous or endocyclic sea-urchins, of the order Endocyclica and class Echinoidea, having a thin round shell with broad ambulacral spaces bearing tubercles and spines, the latter mostly short and pyriform, and oral branchiæ; the typical sea-urchins or sea-eggs. The genera are numerous, such as Echinus, Echinothrix, Toxopneustes, etc.