Delete
Bones
Reference
Mode:
Edit Mode
Menu:
Armature ‣ Delete ‣ Bones
Shortcut:
X
This tool delete selected bones, selected joints are ignored.
If you delete a bone in a chain, its child(ren) will be automatically re-parented to its own parent, but not connected, to avoid deforming the whole armature.
Dissolve
Reference
Mode:
Edit Mode
Menu:
Armature ‣ Delete ‣ Dissolve
Shortcut:
Ctrl-X
Todo 2.76.