The set of diagrams
consisting of an annulus with a finite family of curves connecting some points on the
boundary to each other defines a category in which a contractible closed curve counts
for a certain complex number δ. For δ = 2cos(π∕n) this category admits
a C∗-structure and we determine all Hilbert space representations of this
category for these values, at least in the case where the number of internal
boundary points is even. This result has applications to subfactors and planar
algebras.