• (n.) A saddle-shaped cavity to contain the winter eggs, situated on the back of Cladocera. • (n.) A depression in the sphenoid bone; the pituitary fossa.
E·phip'pi·um noun [ Latin , saddle cloth, from Greek ...; 
ephippium 1. A depression in the sphenoid bone; the pituitary fossa. 2. A saddle-shaped cavity to contain the winter eggs, situated on the back of Cladocera.
a thick shell, consisting of two chitinous plates, that encloses and protects the winter eggs of a cladoceran.