How To Test if a Type is Anonymous?

I have the following method which serialises an object to a HTML tag. I only want to do this though if the type isn't Anonymous.

private void MergeTypeDataToTag(object typeData)
{
    if (typeData != null)
    {
        Type elementType = typeData.GetType();

        if (/* elementType != AnonymousType */)
        {
            _tag.Attributes.Add("class", elementType.Name);    
        }

        // do some more stuff
    }
}

Can somebody show me how to achieve this?

Thanks