Hockey et al. (eds.), 2005, Roberts Birds of Southern Africa, VIIth edn., p. 957, has, "Arnot's Chat Myrmecocichla arnoti ... Named after David Arnot, an attorney at Colesberg, who contributed fossil reptiles, mammals, birds and insects to the South African Museum. Spelling of arnotti corrected to arnoti by Winterhouse & Skead, 1965, Ostrich 36: 147."
Intriguingly, H Chittenden, G Davies & I Weiersbye (2016, Roberts Bird Guide, 2nd edn: 464) list as Arnott's Chat Myrmecocichla arnotti with the following etymology: arnotti = after David Arnott (1822–1894), attorney and naturalist; ... Alt name Arnot's Chat