BCE0005: Unknown identifier: 'Arraylist'.

I'm brand new to scripting and coding overall. I am following a js tutorial book that is having me script for a card matching game. I've had plenty of errors and managed to work most of them out alone and with some help. Currently I have this new error.

Assets/Scripts/GameScript.js(23,29): BCE0005: Unknown identifier: 'Arraylist'.

This is my code

     //#pragma strict
      
     var cols : int = 4; // the number of the columns in the card grid
     var rows : int = 4; // the number of rows in the card grid
     var totalCards : int = cols * rows; //
     var matchesNeededToWin : int = totalCards * .5; //If there are 16, the player needs to find 8 matches to clear the board
     var matchesMade : int = 0; //At the outset, the player has not made any matches
     var cardW : int = 100; // Each card's width and height is 100 pixels
     var cardH : int = 100;
     var aCards : Array; // store all the cards created in this array
     var aGrid : Array; //Array will keep track of the shuffled, dealt cards
     var aCardsFlipped : ArrayList; //This array stores the two cards that the player flips over
     var playerCanClick : boolean; //to determine when player can click or not
     var playerHasWon : boolean = false; // store wether or not the players has won, start as false.
 
     function Start ()
     {
         //sets up the play area
         playerCanClick = true; // allows player to click on cards
         //initialize the arrays as empty lists:
         aCards = new Array ();
         aGrid = new Array ();
         aCardsFlipped = new Arraylist ();
         for (i = 0; i < rows; i++) //creates iterative loop to place rows on grid incrementally
      
      
     aGrid [i] = new Array (); //Create a new, empty array at index i
     for (j=0; j < cols; j++) //creates iterative loop to place cols on grid incrementally
         {
         aGrid [i][j] = new Card (); //places new cards in the play grid
         }
     }
     function OnGUI ()
         {
         GUILayout.BeginArea (Rect(0,0,Screen.width,Screen.height));
         BuildGrid();
         GUILayer.EndArea ();
         print ("building grid!");
         }
      
     class Card extends System.Object
     {
     var isFaceUp : boolean = false;
     var isMatched : boolean = false;
     var img : String = "robot";
     }
      
         function Card()
         {
          
         img = "robot";
         }
     
      
     function BuildGrid ()
     {
     GUILayout.BeginVertical (); //begin building play area placing cards vertically
     for (i =0; i < rows; i++) //places cards incrementally until reaching 4
         {
         GUILayout.BeginHorizantal (); //begin placing cards horizantally
         for (j = 0; j<cols; j++) // places cards in cols horizantlly until reaching 4
             {
             var card : Object = aGrid[i][j];
             if (GUILayout.Button(Resources.Load(card.img), GUILayout.Width(cardW)))
                 {
                 Debug.Log (card.img);
                 }
             }
             GUILayout.EndHorizontal ();
         }
         GUILayout.EndVertical ();
     }

Any help would be greatly appreciated!