An air carrier First Officer reported an ATL Runway 26L incursion at Taxiway B-4. The Captain was distracted and the First Officer did not expect the hold short lines to be at the location or orientation because the Airport diagram depicts them differently.

Narrative

Upon landing Runway 26R ATL we slowed to exit the runway at B-5 high speed. As we approached the intersection we noticed an RJ taxiing East on Taxiway B. We elected to continue the rollout and we exited the Runway at B-3 high speed. While still on the runway we were given taxi instructions to make a left on Bravo and hold short of Runway 26L an B-4. I read back the instructions and as we turned left on Bravo we were told to monitor Tower on 125.32. I tuned the radio and made sure it was the right frequency. We did not have much time to review this route. We had briefed a taxi plan that would take us to the ramp via Bravo and Victor. There was no radio traffic on the 26L Tower frequency while we continued our taxi. I saw an aircraft in position as we approached the hold short. Moments later as we made the turn onto B-4 I realized that we had taxied just past the hold short and I announced to the Captain to 'hold short'. We stopped well short of the runway but beyond the hold line. Moments later we got a call from Tower to hold short and I read the instructions back. Now I saw the aircraft that was in position rolling an Runway 26L. The aircraft lifted off prior to reaching our position on the airport. We crossed the runway as instructed and contacted ground on 121.9 on Taxiway E-3. This is where we were told of a possible deviation and copied the Tower land line number.The airport diagram on the comercial chart 10-9 page depicts a single hold line next to the RWY on B-4 indicating that a turn can be made onto B-4 and hold short of the Runway. In fact this hold line is really two lines in a chevron shape. An aircraft in this location cannot make much of a turn before encountering the hold short line. Since my experience in ATL was to use the parallel Tower's of Charlie or Delta when crossing Runway 26L midfield I was not sure of the location of the hold line at B-4. Also this intersection is NOT depicted as a HOT SPOT. The bottom line is the Captain is taxiing the airplane and the First Officer is monitoring during this phase. Even with CRM and human performance considerations it is impossible to know what someone is thinking and if a Captain thinks he is cleared across a runway and does not verbalize this to the First Officer; then it is very difficult to catch the error before the airplane crosses a hold short line. This is what happened in this case. More CRM is needed so that both pilots know what the situation is and what to expect from the the other pilot.