  In this paper we study abstract shapes of $k$-noncrossing, $\sigma$-canonical
RNA pseudoknot structures. We consider ${\sf lv}_k^{\sf 1}$- and ${\sf
lv}_k^{\sf 5}$-shapes, which represent a generalization of the abstract $\pi'$-
and $\pi$-shapes of RNA secondary structures introduced by
\citet{Giegerich:04ashape}. Using a novel approach we compute the generating
functions of ${\sf lv}_k^{\sf 1}$- and ${\sf lv}_k^{\sf 5}$-shapes as well as
the generating functions of all ${\sf lv}_k^{\sf 1}$- and ${\sf lv}_k^{\sf
5}$-shapes induced by all $k$-noncrossing, $\sigma$-canonical RNA structures
for fixed $n$. By means of singularity analysis of the generating functions, we
derive explicit asymptotic expressions.
