LSJ
οἱ, Dor. for τριακόσιοι, Tab.Heracl. 1.28, 34, al., IG 42(1).110 A 6 (Epid., iv/iii BC), etc. title of the ἔφηβοι at Cyrene, Ammon. Diff. p. 37 V., Hsch. ; corrupted to τριακάπους (acc.) in Eust. 727.18, 1592.57; they are associated with λοχαγοὶ πελταστᾶν, Schwyzer 234.53; — hence τριακατιάρχας, α, ὁ, ib. 14 (Cyrene, iv/iii BC).
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
[ᾱκ], οἱ, die zu einer τριακάς gehörenden ἔφηβοι, Hesych., Eust.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)