Aeneas' son Iulus almost always appears as the last word in a hexameter (e.g. Aen.1.288 dat., 1.556 gen., 7.116 nom., 9.640 acc., 11.58 voc.; Aen.12.185 #cedet Iulus is the exception) and often following parvus (e.g. Aen.2.674 (acc.), 677, 710, 723,...), primus (e.g. Aen.9.232, 9.293,...), pulcher (e.g. Aen.5.570, 7.107, 9.310,...).
This cognomen (Aen.1.267) is trisyllabic (˘ ¯ ¯). Does it perhaps represent ἴουλος (LSJ 'the first growth of the whiskers and beard')? An Athenian may have had this name in IG II^2 2281 (3rd c. AD).