Stephanos of Byzantium - Ethnika
Kassope: a city among the Molossoi, which gives its name to the Kassopian territory. The ethnonym is 'Kassopaios', also 'Kassopios' and 'Kassopia'. The form 'Kassopias' is from 'Kassopios', as in 'Helikonias'. Herodoros says that they are 'Kassopous', perhaps wrongly. All spell it with two 'σ' letters, but Herodian alone with one 'σ'.
Stephanos excerpt (left) is aligned with matched Herodian passages (right). Colors indicate corresponding overlap spans.