This name is a synonym of Linaria aeruginea subsp. pruinosa (Sennen & Pau) Chater & Valdés.
The record derives from WCSP (in review)
(data supplied on 2012-03-23)
which reports it as a synonym with original publication details: Bull. Géogr. Bot. 24: 226 1914.
This name record (from WCSP (in review)) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Linaria supina in version 1 of The Plant List.