This trilobite from the Massie Shale is an exceptionally rare representative of the genus Bumastus, most likely assignable to the species Bumastus ambiguus. Originally, Foerste described this species in 1885 as Illaenus ambiguus from the somewhat older Brassfield Limestone. Since then, both its taxonomic placement and its stratigraphic assignment have been revised. It is not unlikely that the species Bumastus ambiguus also occurs in the Massie Shale, or in the Osgood Formation.
The trilobite itself measures about 16 mm in length and features a remarkably three-dimensional, detailed preservation. In addition, this rare specimen is presented decoratively on its matrix.


BRETT, C.E., CRAMER, B.D., MCLAUGHLIN, P.I., KLEFFNER, M.A., SHOWERS, W.J. & THOMKA, J.R. 2012. Revised Telychian-Sheinwoodian (Silurian) stratigraphy of the Laurentian mid-continent: building uniform nomenclature along the Cincinnati Arch. Bulletin of Geosciences 87(4), 733–753 (11 figures). Czech Geological Survey, Prague. ISSN 1214-1119.
Foerste, A. F. 1885. Descriptions of new trilobite species from the Cincinnati Group. Journal of the Cincinnati Society of Natural History (2nd series), Vol. 8, pp. 130–136.

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