Syntax for method to shape data table into collection of objects (can't get generics right)

Here's what I'm trying to accomplish:

public TCollection<TInterface> ShapeDataTable<TInterface, TImplementation, TCollection>(DataTable dataTable)
      where TImplementation : TInterface
      where TCollection : List
{
    TCollection<TInterface> _returnData = new TCollection<TInterface>();
    if (dataTable.Rows.Count > 0)
    {
        foreach (DataRow row in dataTable.Rows)
        {
            TInterface dataobj = Activator.CreateInstance<TImplementation>();
            ShapeRow<TInterface>(row, dataobj);
            _returnData.Add((TInterface)dataobj);
        }
    }
    return _returnData;
}

I'm getting errors on TCollection:
    "Using the generic type 'System.Collections.Generic.List<T> requires 1 type arguments"
    "The type parameter 'TCollection' cannot be used with type arguments

What do I need to do to get this method compiling?