  We report the identification, in an Extreme Ultraviolet Explorer (EUVE)
spectrum, of a hot white dwarf companion to the 3rd magnitude late-B star Theta
Hya (HR3665, HD79469). This is the second B star + white dwarf binary to be
conclusively identified; Vennes, Berghofer and Christian (1997), and Burleigh
and Barstow (1998) had previously reported the spectroscopic discovery of a hot
white dwarf companion to the B5V star y Pup (HR2875). Since these two
degenerate stars must have evolved from main sequence progenitors more massive
than their B star companions, they can be used to place observational lower
limits on the maximum mass for white dwarf progenitors, and to investigate the
upper end of the initial-final mass relation. Assuming a pure hydrogen
composition, we constrain the temperature of the white dwarf companion to Theta
Hya to lie between 25,000K and 31,000K. We also predict that a third bright B
star, 16 Dra (B9.5V), might also be hiding an unresolved hot white dwarf
companion.
