How to define template routes for a custom element type
You'll need to override the BaseElementType's routeRequestForMatchedElement method in your element type class as follows:

public function routeRequestForMatchedElement(BaseElementModel $element)
{
    return array(
        'action' =&gt; 'templates/render',
        'params' =&gt; array(
            'template' =&gt; '_page',
            'variables' =&gt; array(
                'page' =&gt; $element
            )
        )
    );
}