Luminosity-Diameter Relations for Globular Clusters and Dwarf Spheroidal   Galaxies
  It is shown that globular clusters and the dwarf spheroidal companions of the Galaxy have a different distribution of flattening values, and appear to occupy adjacent regions of the M_v versus log R_h plane that can be separated by what will be referred to as the Shapley line. Surprisingly, typical dwarf spheroidal companions to the Milky Way System are fainter than the average Galactic globular cluster. 
Sidney van den Bergh