  Let $\mathcal{G}$ be an ultragraph and let $C^*(\mathcal{G})$ be the
associated $C^*$-algebra introduced by Mark Tomforde. For any gauge invariant
ideal $I_{(H,B)}$ of $C^*(\mathcal{G})$, we approach the quotient $C^*$-algebra
$C^*(\mathcal{G})/I_{(H,B)}$ by the $C^*$-algebra of finite graphs and prove
versions of gauge invariant and Cuntz-Krieger uniqueness theorems for it. We
then describe primitive gauge invariant ideals and determine purely infinite
ultragraph $C^*$-algebras (in the sense of Kirchberg-R${\o}$rdam) via Fell
bundles.
