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a genus of fossil animals belonging to the shark family, described by the Russian scientist A. P. Karpinskii. Helicoprion was distributed in the early Permian period in the seas that covered the territories of the Urals, Japan, Australia, Spitsbergen, and the United States. The middle (symphyseal) row of teeth in the lower jaw merged into a spiral of two or three turns (hence the name) that protruded from the mouth and was bent on the outside into a cartilaginous cavity. Small crushing teeth in the upper jaw opposed the spiral organ.