A scalloped margin dome is a type of volcanic dome, found on Venus, that has experienced collapse and mass wasting such as landslides on its perimeter. The margins of these domes have  headscarps or 'scallops' separated by ridges that are a consequence of adjoining scallops.
The description refers to a specific geological feature found on Venus called a scalloped margin dome. It explains how these domes have been affected by landslides and the formation of 'scallops' or headscarps along their edges.