Note 240 — Chapter VIII · THE USE OF FICTION IN THE HEROIC POEMS.
Reading edition
The true form is probably Hami-. It is surely far more probable that Ammius is a shortened (hypocoristic) form from the compound name (cf. A.-S. Hemma, Hemmi). But in that case of course we shall have to conclude that the name had been familiar for some time before it came to Jordanes' knowledge.