Bolus (Rchb.f.) 1889 - Bolus H (1889) Contributions to South-African Botany.- Part IV. (With a Revised List of published Species of Extra-tropical South-African Orchids). Journal of the Linnean Society of London, Botany 25(170): 156-210. doi: 10.1111/j.1095-8339.1889.tb00795.x.