The full, uncommented, version of this file is in the demodata directory in file dep.tri.
All lines have the same format:
NODE1 NODE2 NODE3 - the three nodes forming a triangle.
1 2 204 !NODE1 NODE2 NODE3 - the three node numbers for triangle 1 1 204 126 !NODE1 NODE2 NODE3 - the three node numbers for triangle 2 2 3 204 3 4 203 3 203 204 ... 466 468 472 468 469 471 468 471 472 469 470 471