What is "ophidioceras"

Ophidioceras is an alternate name for the Tarphycerid genus Ophioceras, which is known from the Upper Silurian of Europe and North America.

Ophioceras, as this genus is more properly known, has a narrow, evolutly wound, closely coiled shell that diverges in the adult stage. The shell is more or less circular in cross section, strongly annulate with close spaced, rounded, transverse ribs. The venter is bicarinate, with keels along either side separated by a flattened surface. The siphuncle is tubular and thin walled, and may be slightely ventral or dorsal of the center. The adult aperture has deep hypononic and ocular sinuses, not too dissimilar from the Ordovician Lituites, to which this genus is possibly allied.

Some 12 species have been described which have been reduced to two, Ophioceras rudens Barrande, 1865 and O. simplex Barrande, 1865 with two subspecies, O. simplex simplex and O. s. proximum. Minor evolutionary changes can be observed within both species, which In spite of their widespread distribution do not demonstrate any major geographical variations.