Hi Dennis - great simulator and not a bad shot of Mars there either.
Have a check again of the identification you have for Mare Sirenum as I pretty sure that's actually further around the planet (toward the extreme right on you image or even beyind the limb). The dark extension you've got tagged there is Sinus Sabeus with the very end bit called Sinus Meridani (which I believe is where one of those Mars crawly things is right now).
cheers,