Do you mean something like that?!
var myList = new Dictionary<String, List<String>>();
myList.Add("row1", new List<String>());
myList.Add("row2", new List<String>());
myList.Add("row3", new List<String>());
myList["row1"].Add("cat");
myList["row1"].Add("dog");
myList["row1"].Add("rat");
myList["row2"].Add("bus");
myList["row3"].Add("sunday");
myList["row3"].Add("monday");
myList["row3"].Add("tuesday");
myList["row3"].Add("friday");
Console.WriteLine("Number of rows -> " + myList.Count);
foreach(var row in myList) {
Console.WriteLine("Number of columns in " + row.Key + " -> " + row.Value.Count);
}
[edit]fleshing out solution[/edit]