Rimae Sirsalis is a lunar rille. Rimae Sirsalis cuts across highlands almost exclusively. It starts at the edge of Oceanus Procellarum near the modest crater Sirsalis from which it gets its name and proceeds directly away from the mare, eventually ending up among the cracks in the floor of the crater Darwin. (wikipedia entry)
A rima is a fissure. On the Moon they are named after nearby craters.