 Arthur Smith Woodward formally synonymized "M. peachi" and "M. coriaceus" in 1891.In 2015 a study published in PeerJ reassessed the two remaining Middle Devonian species ("M. pusillus" and "M. peachi") and found that they also could not be distinguished from one another.Hence, only two species from the Orcadian Basin and Midland Valley areas of Scotland are currently considered to be valid