Mecynoceras is a genus of Late Devonian oncocerids included in the Poterioceratidae, a family of subcircular to compressed exogastric cyrtocones without a hyponomic sinus.

Mecynoceras has a compressed, gibbous cyrtoconic shell.

Septa are transverse, close spaced; the siphuncle large, subcentral, with actinosiphonate deposits.

Cyrtogomphus, Lysagoroceras, and Poterioceras are among related genera.

This prehistoric nautiloid-related article is a stub.