Archipterygium

Ar`chip`te`ryg´i`um

    (är`kĭp`tė`rĭj´ĭ`ŭm)
n.1.(Anat.) The primitive form of fin, like that of Ceratodus.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.