We present optical and X-ray observations of two tidally distorted , extremely low-mass white dwarfs ( WDs ) with massive companions .
There is no evidence of neutron stars in our Chandra and XMM observations of these objects .
SDSS J075141.18 - 014120.9 ( J0751 ) is an eclipsing double WD binary containing a 0.19M _ { \sun } WD with a 0.97M _ { \sun } companion in a 1.9 h orbit .
J0751 becomes the fifth eclipsing double WD system currently known .
SDSS J174140.49+652638.7 ( J1741 ) is another binary containing a 0.17M _ { \sun } WD with an unseen M \geq 1.11 M _ { \sun } WD companion in a 1.5 h orbit .
With a mass ratio of \approx 0.1 , J1741 will have stable mass transfer through an accretion disk and turn into an interacting AM Canum Venaticorum ( AM CVn ) system in the next \approx 160 Myr .
With a mass ratio of 0.2 , J0751 is likely to follow a similar evolutionary path .
These are the first known AM CVn progenitor binary systems and they provide important constraints on the initial conditions for AM CVn .
Theoretical studies suggest that both J0751 and J1741 may create thermonuclear supernovae in \sim 10 ^ { 8 } yr , either .Ia or Ia .
Such explosions can account for \sim 1 % of the Type Ia supernova rate .