and the Galaxy.

We use the Millennium Simulation to construct samples of mock Milky Way/Andromeda galaxies and of mock Local Groups as follows. We begin by identifying all Type 0 or Type 1 galaxies with characteristic “rotation velocity” either in the narrow range $200 \le V_{max}< 250{{\rm \,km\,s^{-1}}}$ or in the wider range, $150 \le V_{max}< 300{{\rm \,km\,s^{-1}}}$. This produces samples of $166,090$ and $699,177$ galaxies respectively. The exclusion of Type 2 galaxies reduces the samples by about 5-6% in each case, but the excluded galaxies are in any case not plausible analogues for the Local Group giants since they are almost all members of large groups or clusters. We also consider subsamples in which the morphologies predicted by the semianalytic model are forced to approximate those of M31 and the Galaxy. Specifically, we require a bulge-to-total luminosity ratio in the range $1.2 \le M_{B,bulge}-M_{B,total}
< 2.5$ so that the disks are 2 to 9 times brighter than the bulges in the *B*-band. This morphology cut reduces the samples in the two $V_{max}$ ranges to $62,605$ and $271,857$ galaxies respectively.

We then identify Local Group analogues in each of these four samples by identifying isolated pairs with separations in the 