For these coins I use as a reference L.
Travaini, La Monetazione nell'Italia Normanna, (Istituto Storico Italiano
per il Medio Evo - Nuovi Studi Storici - 28),
Rome 1995.
Your coin is n. 368 on p. 317.
The
obverse is the
face with the arabic/cufic
inscription (your photo has it upside down...)
The
reverse is the
face with the latin
inscription.
The inner
circle of the
obverse: al-malik Ghulyalim (al-thani) al-musta'izz bi-illah = the
king William (the second) powerful by the grace of God.
The outer
legend of the
obverse (cufic characters): duriba bi-amr al-malik al-mu'azzam al-musta'izz bi-llah = struck by the order of the
king the great strong by the grace of God
The inner
circle of the
reverse: °
REX W SCDS
The outer
legend of the
reverse: + OPERATA IN URBE MESSANE