Pytheas is a small lunar impact crater located on the southern part of the Mare Imbrium, to the south of the crater Lambert. It has a sharply defined rim, a hummocky outer rampart, and an irregular interior due to slumping or fall-back. There is a small crater along the northern outer rampart, and a similar crater about 20 km to the west. The crater possesses a small ray system that extends for a radius of about 50 kilometers. (wikipedia entry)