Hi Erich,
Actually the ones with the yellow markings are the "typical" form of the
species (Drupa ricinus ricinus).  The ones without the markings, with a pure
white aperture, are called Drupa ricinus albolabris.  In most locaities, the
yellow form is the more common one.  But apparently the albolabris form
dominates where you were collecting.
Paul M.