Reflection Filter types by Generic Base

I'm trying to reflect into an assembly and get out all of the types who derive from a generic type.

protected List<Assembly> _assemblies = new List<Assembly>(); 

public List<Type> FilterByType<T>()
{
    return this._assemblies.SelectMany(x => x.GetTypes()).Where(type => typeof (T).IsAssignableFrom(type)).ToList();
}

However when I try to call the filter method I cannot pass a Type-Less Generic

// This does not compile because it's an unbound generic
FilterByType<AbstractValidator<>>()

How can I Filter where any of my bases are a derrive from a generic?