Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ăpelles, is (voc. Apella, Plaut. Poen. 5, 4, 101, as if from the Doric Ἀπελλᾶς), m., = Ἀπελλῆς, a distinguished Greek painter in the time of Alexander the Great, Plin. 35, 10, 36, § 10; Cic. Brut. 18, 70; id. Off. 3, 2, 10; id. Fam. 1, 9; Prop. 4, 8, 11 al.
Hence, Ăpellēus, a, um, adj., of or belonging to Apelles: opus, Mart. 7, 83: tabulae, Prop. 1, 2, 22 al.