Lewis & Short

Memnon, ŏnis, m., = Μεμνων, son of Tithonus and Aurora, and king of the Ethiopians; he went to the aid of the Trojans, and was slain by Achilles: nigri Memnonis arma, Verg. A. 1, 489.
When burned on the funeral pile he is said to have been changed by Aurora into a bird, while from his ashes many other birds flew up, called Memnoniae or Memnonides, who every year flew from Ethiopia to Troy and fought over Memnon’s tomb, Ov. M. 13, 600 sq.; id. ib. 13, 617; Plin. 10, 26, 37, § 74. The black marble statue of Memnon, near Thebes, when struck by the first beams of the sun, gave forth a sound like that of a lute-string, which was regarded as Memnon’s greeting to his mother: dimidio magicae resonant ubi Memnone chordae, Juv. 15, 5; cf.: mater lutea Memnonis, i. e. Aurora, Ov. F. 4, 714: Memnonis saxea effigies, Tac. A. 2, 61.
The fate of Memnon was the subject of a poem by Alpinus, Hor. S. 10, 36.
Hence,

  1. A. Memnŏnĭus, a, um, adj., of or belonging to Memnon, Memnonian.
    1. 1. Lit.: Memnoniae aves, Sol. 40.
    2. 2. Transf., Oriental, Moorish, black (poet.): color, Ov. P. 3, 3, 96: regna, Luc. 3, 284.
      Esp., as subst.: Memnŏnĭa (Menn-), ae, f., a precious stone, of a black color, Plin. 37, 10, 63, § 173.
  2. B. Memnŏnĭ-des, um, f. plur., the birds of Memnon; v. supra.