  We revisit a nonlinear spline primitive for 3-space first studied by Even
Mehlum. It is the spherical clothoid, the spherical curve with geodesic
curvature a linear function of arc length. We present its Cartesian coordinate
functions using confluent hypergeometric functions (the Kummer functions) and
its stereographic projection onto the complex plane. New Humbert series results
are also presented along with generating function formulas related to the
associated Meixner-Pollaczek polynomials.
