  I report spectroscopy and time-series photometry of the cataclysmic binary
CSS J134052.0+151341. The optical light is dominated by the secondary star,
which I classify as K4 (+-2 subclasses), yet the orbital period derived from
the absorption radial velocities is only 2.45 hr, implying a Roche radius much
too small to contain a main-sequence K star. The spectrum shows enhanced sodium
absorption in several lines, suggesting that the surface material has been
processed at high temperatures. CSS J134052.0+151341 appears to be a rare
example of a cataclysmic binary in which the secondary star is the stripped
core of a formerly much more massive star, that began mass transfer after much
of the core's nuclear evolution had taken place.
