Custom meta box not showing up

I’ve created a custom post type and now need to attach a custom meta box to the edit context. The code I’ve cobbled together is not doing anything that I can see.

Here’s some of the relevant bits:

class Fixtures {
   public function __construct() {
      add_action( 'init', array(&$this,'create_post_type'));
      add_action( 'add_meta_box', array(&$this,'fixtures_add_custom_meta_box'));
   }

   function create_post_type() {
      /* code works - omitted */
   }

   public function fixtures_add_custom_meta_box() {
	error_log( __FUNCTION__ );   // never shows up in debug.log
	add_meta_box(
            'fixtures-metabox'
            ,'Fixture Attributes'
            ,array(&$this, 'render_custom_meta_box')
            ,'post'
            ,'normal'
            ,'high'
        );
    }

    public function render_custom_meta_box() {
    	error_log( __FUNCTION__ );     // never shows up in debug.log
    	 wp_nonce_field( plugin_basename( __FILE__ ), 'fixtures_noncename' );

    	 // the actual fields presented by the meta_box
    	 // - potential parents - only none, other fixtures
    	 // - ordering number
    	 // we omit the template option for now to simplify the plugin

    	 $value = get_post_meta( $post->ID, '_fixtures_parent_id', true );
    	 echo '<label for="fixtures_parent_id">';
    	 echo 'Parent Fixture';
    	 echo '</label> ';
    	 echo '<input type="text" id="fixtures_parent_id" name="fixtures_parent_id" value="'.esc_attr($value).'" />';

    	 $value = get_post_meta( $post->ID, '_fixtures_order', true );
    	 echo '<label for="fixtures_order">';
    	 echo'Order';
    	 echo '</label> ';
    	 echo '<input type="text" id="fixtures_order" name="fixtures_order" value="'.esc_attr($value).'" size="4" />';
    }
}

$fixtures = new Fixtures();

Any insights greatly appreciated.
~ Erik