Based on an accurate computation of the first 1851 quantal energy levels of
the truncated hyperbola billiard, we have found an anomalous long-range
modulation in the integrated level density. It is shown that the observed
anomaly can be explained by an additional term in Gutzwiller's trace formula.
This term is given as a sum over families of closed, non-periodic orbits which
are reflected in a point of the billiard boundary where the boundary is
continuously differentiable, but its curvature radius changes discontinuously.Comment: 8 pages, uu-encoded ps-fil