/het'euh ros"treuh keuhn/ , n. Paleontol.
any of several ostracoderms of the order Heterostraci, from the Silurian and Devonian Periods, having the anterior part of the body enclosed in bony plates.
[ Heterostrac ( i ) (pl.) name of the order, equiv. to heter- HETER- + Gk ostrak ( ón ) (sing.) shell + -AN ]