This name is a synonym of Mimulus angustatus (A. Gray) A. Gray.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50102638) with original publication details: Proc. Amer. Acad. Arts 7: 38 1868.
This name was in version 1 of The Plant List, record tro-50102638, and has not been changed.