Xml Serialization using xsd:type

This is what I want:

<shareParcels>
<shareParcel>
  <shareholders xmlns:xsi="http://ift.tt/ra1lAU" xsi:type="individualRole">
    <physicalAddress>
      <addressLines>17, 4f, Crownlynn Place</addressLines>
      <addressLines>New Lynn</addressLines>
      <addressLines>Auckland</addressLines>
      <countryCode>NZ</countryCode>
    </physicalAddress>
    <firstName>Lei</firstName>
    <lastName>NIU</lastName>
  </shareholders>
  <numberOfShares>100</numberOfShares>
</shareParcel>

This is what I get:

  <shareParcels>
<shareParcel>
  <shareholders>
    <individualRole>
      <physicalAddress>
        <addressLines>17, 4f, Crownlynn Place</addressLines>
        <addressLines>New Lynn</addressLines>
        <addressLines>Auckland</addressLines>
        <countryCode>NZ</countryCode>
      </physicalAddress>
      <firstName>Lei</firstName>
      <lastName>NIU</lastName>
    </individualRole>
  </shareholders>
  <numberOfShares>100</numberOfShares>
</shareParcel>

This is the code I have:

    public class ShareParcel {
    [XmlArray("shareholders")]
    [XmlArrayItem("entityOrganisationRole", typeof(EntityOrganisationRole))]
    [XmlArrayItem("entityOrganisationShareholder", typeof(EntityOrganisationShareholder))]
    [XmlArrayItem("individualRole", typeof(IndividualRole))]
    [XmlArrayItem("disqualifiedDirector", typeof(DisqualifiedDirector))]
    [XmlArrayItem("individualShareholder", typeof(IndividualShareholder))]
    [XmlArrayItem("directorShareholder", typeof(DirectorShareholder))]
    [XmlArrayItem("director", typeof(Director))]
    public List<Role> Shareholders { get; set; }

    [XmlElement("numberOfShares")]
    public long NumberOfShares { get; set; }
}

I can't seem to figure out how to make the serilizer use the xsd:type attribute for inherited type of Role?

Thanks in advance,