Samual,
 
Seahorses should be laid out on a couple of pieces of paper towel to dry
out.  As for your broken sand dollars, there is an old trick to help with
the preservation of these guys.  Soak your sand dollars (we are assuming
these are dead, bleached white sand dollars) in a mixture of Elmer's glue
(or any other white glue I suppose) and water).  The mixture is probably no
more than 1 part glue to five or more parts water.  I just squirt a bunch of
glue in the water, stir until dissolved and then leave the sand dollars in
the mixture overnight.  When you bring them out, pat them dry with a paper
towel and then let them really dry out on a sheet of wax paper.  This should
greatly strengthen your sand dollars -- although they will always be a bit
fragile.
 
Tom Eichhorst in New Mexico, USA