The plural of ail adjectives in the féminine is regular

89. Adjectives whose last letter is s, or x do not take the plural sign s.

90. Adjectives ending in -eau replace the regular plural sign s by x: beau, plur. beaux.

91. Matinal cannot be used in the plural as a masculine; only the plural féminine matinales is used.

92. Adjectives ending in -al form their plural by substituting -aux to -al, e.g.:

national (national) plur.: nationaux IRREGULAR COMPARATIVES