Removing Missing Objects From A List

Hello, I have a list:

   public var enemies : List.<GameObject> = new List.<GameObject>();

That I put all of the enemies in a certain area in

 var hitColliders : Collider[] = Physics.OverlapSphere (transform.position, circleRadius);
  for (var hit : Collider in hitColliders) {//Converts Collider[] to Collider        
      if(hit.gameObject.tag == "Killable"){//Detects if it is an enemy.
  if(EnemyScript.added == false){//So it will not add a second time.
       enemies.Add(hit.gameObject);
       EnemyScript.added = true; 
    }
 }

In this list I get the number of enemies in the area, so I will know to spawn them in if it is less than the allotted amount.

 EnemiesInSection = enemies.Count;

The Problem is that when a enemy dies, in the list, the game object comes up missing, where I would like to remove it.

I have tried putting a boolean in my enemy script that when it dies it comes up true and then use enemies.remove(hit.gameObject) and that did not work.

I also tried doing this:

 if(hit.gameObject == null){
         enemies.Remove(hit.gameObject);
         }

How would I go about removing the enemies once they die.

All help is appreciated, Thanks

Thor