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. The venter, especially of the chambered phragmocone is convex in profile; the body chamber long and tubular. Septa are transverse, close spaced; the siphuncle large, subcentral, with actinosiphonate deposits. , , and are among related genera.