porcellanidæ

from The Century Dictionary.

• A family of short-tailed ten-footed crustaceans, typified by the genus Porcellana, so called from the smoothness and hardness of the shell; the porcelain-crabs. The antennæ are very long, and the chelæ of great size.
• In conchology, a family of gastropods: commonly called Marginellidæ.