The Wikipedia article on the Lunar crater Alphonsus includes the following remark:
What does "cinder-shaped" mean?The floor is fractured by an elaborate system of rilles and contains three smaller craters surrounded by a symmetric darker halo. These dark-halo craters are cinder-shaped and are believed by some to be volcanic in origin, although others think they were caused by impacts that excavated darker mare material from underneath the lighter lunar regolith.
Here's a photograph of the crater (click on the photo for an enlrged version). The three craters referred to are clearly visible: one of them is at the five-o'clock position, and the other two are around the two-o'clock position.