  We report the discovery of a hot DQ white dwarf, NGC 2168:LAWDS 28, that is a
likely member of the 150-Myr old cluster NGC 2168 (Messier 35). The spectrum of
the white dwarf is dominated by CII features. The effective temperature is
difficult to estimate but likely > 20,000 K based on the temperatures of hot
DQs with similar spectra. NGC2168:LAWDS 28 provides further evidence that hot
DQs may be the ``missing'' high-mass helium-atmosphere white dwarfs. Based on
published studies, we find that the DBA WD LP 475-242 is likely a member of the
Hyades open cluster, as often assumed. These two white dwarfs are the entire
sample of known He-atmosphere white dwarfs in open clusters with turnoff masses
>2 solar masses. Based on the number of known cluster DA white dwarfs and a
redetermination of the H-atmosphere:He-atmosphere ratio, commonly known as the
DA:DB ratio, we re-examine the hypothesis that the H- to He-atmosphere ratio in
open clusters is the same as the ratio in the field. Under this hypothesis, we
calculate that five He-atmosphere WDs are expected to have been discovered,
with a probability of finding fewer than three He-atmosphere white dwarfs of
0.08, or at the ~ 2-sigma level.
