The maker of your plate was Richard-Emile Agu, mark a horse head between two dials (une tête de cheval entre deux molettes). Agu, a hollowware maker, worked in Paris on rue St-Honoré, first registering a mark in 1805-1806. In 1813 he was on the Île St-Louis, terrain des Capucins. No end date is given. Your plate can be dated with some exactitude from between 1805, when Agu first registered, and 1809, the end of the period shown by the standing cock in an octagonal reserve. It appears to have been an under plate for a tureen or other vessel, with decoration in the Empire style.
Hope this helps.
See Arminjon, v I, no. 03142, p. 308.