This is the XHS-9-Si-160-T transducer that was originally shipped out with the 981/987c Si units.
The 898, 997, 998, 1197 and 1198 units also support the full usage of this older transducer if you set the Transducer Select menu to the SideScan menu setting (262/455kHz Si/Di sonar, 50/200kHz 2D sonar).