Lattice: xyplot group title format

Dear all,

if I plot a lattice xyplot like:

library(lattice); require(stats);
Depth <- equal.count(quakes$depth, number=8, overlap=.1)

xyplot(lat ~ long | Depth, data = quakes)


How can I manipulate the group title format (here: Depth)? Like the font size, position, etc.

Best
Marcus