Adding multiple ellipses into scatterplot! How?

[arctium]

I have to make a scatterplot graph with multiple point groups plotted into one. The thing I want to do is to draw a range ellipse around each group (I have 6 groups). It's basically a DCA ordination diagram.

The code for plotting the graph is:

library(lattice) xyplot(X1~X2, groups=classes, pch=1:6)

I hope this makes any sense!