[dotNetRDF-bugs] Calling CreateOntologyClass bug

[<c.c...@gm...>]

Hy, I´m Carmelo Cacciato
I´m developing a new class to model an ontology. i need to write in a file .owl new classes.
i´m using this sintax
OntologyGraph  graph = new OntologyGraph();

OntologyOntology superClass = graph.CreateOntologyClass(newUri(string uriSuperClass));
OntologyClass subClass = graph.CreateOntologyClass(new Uri(string uriSubClass));
superClass.AddSubClass(subclass);

when i save the file i don´t get a class but a tag of a description.

<rdfs: Description  ............>
< rdf: subClassOf ..........     superClass
</Description>

but i need tag
<Class

/Class>
Can i have an answer? 

thanks to all.