  I find an explicit description of modular units in terms of Siegel functions
for the modular curves $X^+_{ns}(p^k)$ associated to the normalizer of a
non-split Cartan subgroup of level $p^k$ where $p\not=2,3$ is a prime. The
Cuspidal Divisor Class Group $\mathfrak{C}^+_{ns}(p^k)$ on $X^+_{ns}(p^k)$ is
explicitly described as a module over the group ring $R =
\mathbb{Z}[(\mathbb{Z}/p^k\mathbb{Z})^*/\{\pm 1\}]$. In this paper I give a
formula involving generalized Bernoulli numbers $B_{2,\chi}$ for
$|\mathfrak{C}^+_{ns}(p^k)|$.
