Here's a solution defining a new list environment descenum with enumitem. The descenum environment is basically the same as an enumerate environment, but in this environment (and only there) the \item command is modified to take an argument, which is placed between parentheses after the number of the enumerated item.
A short example:
\documentclass{article}
\usepackage{enumitem}
\newlist{descenum}{enumerate}{1}
\setlist[descenum]{%
label={\arabic*},
before={\changeitem},
after={\renewcommand{\item}{\olditem}},
}
\newcommand{\changeitem}{%
\let\olditem\item
\renewcommand{\item}[1]{\olditem (##1).\ }
}
\begin{document}
\begin{descenum}
\item{First thing to be described} First description.
\item{Second thing to be described} Second description.
\end{descenum}
\end{document}

If you want to change how the described items are displayed, you can modify the \changeitem command, which renews the \item command. For example, if you want the described things to be in italic, you could replace
\newcommand{\changeitem}{%
\let\olditem\item
\renewcommand{\item}[1]{\olditem (##1).\ }
}
with
\newcommand{\changeitem}{%
\let\olditem\item
\renewcommand{\item}[1]{\olditem (\textit{##1}).\ }
}