65 in Virgo\]. In general, these nearby systems contain one or two large galaxies along with small satellites; they are therefore different in character from the other RSCG’s and from the HCG’s. To exclude these systems, in later Sections we ignore nearby groups ($cz \leq 2300$ km s$^{-1}$) when exploring the environments of RSCG’s and when calculating the compact group selection function.

Hickson required $\overline{\mu}_{G} < 26.0$, where $\overline{\mu}_{G}$ is the surface brightness in E, for the POSS plates, of the group in magnitudes arcsec$^{-2}$. We translate this criterion as $\overline{\mu}_{G,{\rm Zw}} < 27.7$ using arguments from Prandoni, Iovino & MacGillivray (1994) that a surface brightness of 26.0 magnitudes arcsec$^{-1}$ in $E$ is equivalent to a surface brightness of 27.7 magnitudes arcsec$^{-1}$ in $b_{j}$ which is similar to the Zwicky magnitude scale. Four of our compact groups do not meet this requirement. All of these groups are in the CfAnorth survey. They are nearby ($cz \leq$ 1200 km s$^{-1}$), and have large angular radii ($\theta_{G} > 14 '$). All of these groups fail the isolation criterion as well.

Isolation Criterion
-------------------

Hickson’s isolation criterion has complex physical implications. In a survey of compact groups selected on the sky, interloping galaxies 