Ephippium

from The Century Dictionary.

• noun In anatomy, the sella turcica or pituitary fossa of the human sphenoid bone, or other formation or appearance likened to a saddle.
• noun In branchiopods, as Daphnia, an altered part of the carapace, of a saddle-shaped figure, representing a large area over which both inner and outer layers of the integument have acquired a brownish color, more consistency, and a peculiar texture. It is an alteration due to the development of that kind of egg known as ephippial.
• noun [capitalized] In entomology, a genus of brachycerous dipterous insects, of the family Stratiomyidæ. The larvæ of E. thoracicum are found in ants' nests.
• noun [capitalized] A genus of mollusks.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Anat.) A depression in the sphenoid bone; the pituitary fossa.
• noun (Zoöl.) A saddle-shaped cavity to contain the winter eggs, situated on the back of Cladocera.