  In this paper we first of all determine all possible genera of (odd and even)
definite unimodular lattices over an imaginary-quadratic field. The main
questions are whether the partial class numbers of lattices with given Steinitz
class within one genus are equal for all occuring Steinitz classes and whether
the partial masses of those partial genera are equal. We show that the answer
to the first question in general is "no" by giving a counter example, while the
answer to the second question is "yes" by proving a mass formula for partial
masses. Finally, we determine a list of all single-class partial genera and
show that a partial genus consists of only one class if and only if the whole
genus consists of only one class.
