The Roman Map of Britain Stuctius  River Ystwyth, Cardiganshire

Iuctius (R&C 247) next
Stoukkia Stuccia, vars. Stoukia Stucia, Soukkia Succia, Toukkia Tuccia, Stoulkia Stulcia (Ptolemy II 3 2)

The Cosmography's form Iuctius (for Stuctius) is the result of the initial long s being taken as a text divider (/) and discarded, then the t mistaken for I .