  C. Giller proposed an invariant of ribbon 2-knots in S^4 based on a type of
skein relation for a projection to R^3. In certain cases, this invariant is
equal to the Alexander polynomial for the 2-knot. Giller's invariant is,
however, a symmetric polynomial -- which the Alexander polynomial of a 2-knot
need not be. After modifying a 2-knot into a Montesinos twin in a natural way,
we show that Giller's invariant is related to the Seiberg-Witten invariant of
the exterior of the twin, glued to the complement of a fiber in E(2).
