using System.Collections.Generic;
using System.Linq;

public partial class _Default : System.Web.UI.Page
{
    [System.Web.Services.WebMethod]
    public static IEnumerable<Foo> GetData(int startIndex)
    {        
        startIndex = startIndex * 80;
        return Enumerable.Range(startIndex, 80).Select(i => new Foo { Bar = "works-on-my-machine-starburst.png" });
    }

    public class Foo
    {
        public string Bar { get; set; }
    }
}