Wow! So many kind responses! About the size of the juvenile
C. lubrica; I was real tired last night, and I just made a crude (and
totally
inaccurate) estimate. They are really about 3mm. I will try some various
greens, but, like Kurt said, they might feed on microalgae. It would be
interesting
to find out their diet. I have plenty of eggshells, and I will just put
them in the blender
and set it on "liquify" to make powder. That thing about lubrica living
in leaf-filled gutters
is neat; I saw a few VERY TINY (1mm) specimens on the undersides of dead
leaves the
other day; the leaf could be like a sail, and be blown up on the roof
with the snails on it.
Anyway, I give my thanks for the help you all provided; I will keep
everyone updated on the
snails' progress.

Kind Regards,
James