ratitæ

from The Century Dictionary.

• One of the prime divisions of birds, including the ostriches, cassowaries, emus, and kiwis; the group of struthious birds, as contrasted with Carinatæ, to which all other existing birds belong.

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

• noun plural (Zoöl.) An order of birds in which the wings are small, rudimentary, or absent, and the breastbone is destitute of a keel. The ostrich, emu, moa, and apteryx are examples.