The giant puffball, Calvatia gigantea, is easily recognized by its size and shape. Typical specimens are about the size of a soccer ball, and more or less round. However, it can be much larger (a 5-foot, 50-pound specimen is on record!), and its shape can be more "blob-ish" than round, especially when it attains enormous sizes. But it is never shaped like an inverted pear, since it lacks the sterile base portion common to many other puffballs. (Link)