lie along the hottest canonical post-HB track at a point where the evolution is relatively slow. However, things are less simple for W8750. While it lies close to the post-HB track of a late hot flasher with a 10$^{-5}$  hydrogen surface layer, it also lies at a point where the evolution is rapid. Moreover, it is difficult to understand why W8750 has a helium-poor surface when the other stars with possible flash mixing are much more helium-rich. In order to place it on the least massive canonical track (where evolution is slow in this temperature range), its gravity would have to be overestimated by about 0.4 dex, which is about 3$\sigma$.

[psfile=0505\_9.ps hscale=95 vscale=95 hoffset=-70 voffset=-350 angle=0]{}

W23198 is a less clear case: In Figs. \[ngc2808\_tg\] and \[ngc2808\_the\] it lies at the cool end of the population of helium-enriched stars, but well separated from the canonical EHB stars. Judging from its position in Fig. 9, W23198 may be a late hot flasher with very high hydrogen content and/or effective diffusion or an example for shallow mixing (see below).

Helium-Rich Stars
-----------------

The parameters of the helium-rich stars provide support to the late hot flasher scenario: Figs. \[ngc2808\_tg\] and \[ngc2808\_the\] show 