Parry arcs

A halo in the form of arcs that appear outside the upper and lower tangent arcs to the halo of 22°.

The columnar crystals have their long axes horizontal, which by itself would produce the tangent arcs, and a prism face horizontal.
See minimum deviation, anthelic arcs.
Humphreys, W. J. 1940. Physics of the Air. 3d ed., . 524–526.