David,
This was an intriguing puzzle so I had a look too. Meurig is correct that he appears on the roll for the 2nd Dorsetshire Regiment under different names;
QSA roll. WO100/189 p8. 657 Pte Batram, T. Clasps CC, OFS, Tr and Laing's Nek. A note says 'Send home for discharge, time expired'.
Supplementary roll. WO100/189 p84. 657 Pte Bertram, T. SA01 clasp. Note says 'Discharged. Time expired'.
This points up one of the shortcomings of the Ancestry indexing. The QSA entry appear in the Ancestry index as 'Beltram, T" and the Supplementary as 'Bertram, S'. Coincidentally this is the second such error this evening. Looking for H Willis, Ancestry's entry was H Willes. No wonder it took some time to find him. In both cases, searching for regimental number and regiment was more successful.
Regards
David