  We describe the ROSAT All-Sky Survey-Center for Astrophysics Loose Systems
(RASSCALS), the largest X-ray and optical survey of low mass galaxy groups to
date. We draw 260 groups from the combined Center for Astrophysics and Southern
Sky Redshift Surveys, covering one quarter of the sky to a limiting Zwicky
magnitude of 15.5. We detect 61 groups (23%) as extended X-ray sources.
  The statistical completeness of the sample allows us to make the first
measurement of the X-ray selection function of groups, along with a clean
determination of their fundamental scaling laws. We find robust evidence of
similarity breaking in the relationship between the X-ray luminosity and
velocity dispersion. Groups with sigma < 340 km/s are overluminous by several
orders of magnitude compared to the familiar LX ~ sigma^4 law for higher
velocity dispersion systems. An understanding of this break depends on the
detailed structure of groups with small velocity dispersions sigma < 150 km/s.
