When my wife and I visited Bouchoir Cemetery back in 1999 searching for the last resting place of my grandfather, Sergeant Thomas Bashforth, B Company, 11th DLI, we adopted the headstone of an unknown DLI soldier in a group of unknowns alongside Private John Kennedy (page 237 of the book). The body of Thomas Bashforth was never identified, but if he is buried in a cemetery anywhere it is most likely at Bouchoir, a mile or so from where he fell at Arvillers.
The Commonwealth War Graves Commission website now has much more information available for casualties, including report forms made by those involved after the War in creating the concentration cemeteries such as that at Bouchoir. I discovered this while checking some information for a descendant of a 7 DCLI man, Harold Masters (who is buried there). I have now been able to relate the map reference given in the concentration report for ‘my grave’ to the appropriate grid references on the trench map 66E NE, only to find that the location is near Mézieres, some distance away from Arvillers.
The battalion was involved with others from 20th Division in an attempt to retake the village on Good Friday, 29 March 1918. Whoever this man was must have been buried where he fell, somewhere in ‘Wheelbarrow Wood’ just to the north west of the village. It is possibly one of four men: Lt Frederick Arnott, or Privates Joseph Barnard, John O’Brien and Clifford Pollard. The two ‘unknown soldiers’ from my group were found in the same general vicinity but may have been from another regiment. Pte Kennedy was moved from what had probably been a field hospital burial ground near the village (he died on 25 March 1918, before the battles reached this spot).
So the search for the last resting place of Thomas Bashforth continues, though some judicious searching of the CWGC website might just come up with a grid reference for the ground in front of Arvillers. Meanwhile I will continue to hold the same headstone as a temporary marker – I am sure he is not far away!
 This is available on line from the National Library of Scotland, along with a good selection of other maps.