Lisp Help

I was wondering if it is possible to set default values for parameters in lisp (specifically scheme) like you can in C++.
Or is it best to just create a second procedure that passes in, for example, the first two parameters and a default value into my original procedure?
I hope that made sense.
Before someone suggests I read SICP, I am halfway through the chapter on Data Abstraction.

>>10
Do you have a reason for using 65535, or do you just not realise Scheme deals with arbitrary-size integers?