Get details about a role that is a group member

var webClient = new WebClient();

// replace the "admin" and "Admin's API key" with your valid user and apikey!
// http://telligent.com/community/developers/w/wiki/how-to-generate-an-api-key.aspx
var adminKey = String.Format("{0}:{1}", "Admin's API Key", "admin");
var adminKeyBase64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(adminKey));

webClient.Headers.Add("Rest-User-Token", adminKeyBase64);

var requestUrl = "http://mysite.com/api.ashx/v2/groups/3/members/roles/1089.xml"; // or .json
var xml = webClient.DownloadString(requestUrl);

Console.WriteLine(xml);

<?xml version="1.0" encoding="utf-8"?>
<Response>
  <Info />

  <Warnings />
  <Errors />
  <Role>
    <Id>1089</Id>
    <Name>Some Role Name</Name>

    <Description>description</Description>
    <GroupId>53</GroupId>
    <IsSystemRole>false</IsSystemRole>
    <MembershipType>Member</MembershipType>

  </Role>
</Response>

{
  "Role": {
    "Name": "Some Role Name",
    "Description": "description",
    "GroupId": "53",
    "IsSystemRole": "false",
    "MembershipType": "Member"

    "Id": 1089
  },
  "Info": [],
  "Warnings": [],
  "Errors": []
}