  We have developed an improved algorithm that allows us to enumerate the
number of site animals (polyominoes) on the square lattice up to size 46.
Analysis of the resulting series yields an improved estimate, $\tau =
4.062570(8)$, for the growth constant of lattice animals and confirms to a very
high degree of certainty that the generating function has a logarithmic
divergence. We prove the bound $\tau > 3.90318.$ We also calculate the radius
of gyration of both lattice animals and polygons enumerated by area. The
analysis of the radius of gyration series yields the estimate $\nu =
0.64115(5)$, for both animals and polygons enumerated by area. The mean
perimeter of polygons of area $n$ is also calculated. A number of new amplitude
estimates are given.
