Craterlike appearance of colonies of Streptococcus pneumoniae (colonies having the characteristic flattened center). Rapid growth is frequently followed by autolysis and colonies begin to lyse in the center and even disappear. This is caused by their susceptibility to autolytic enzymes and to peroxides produced during growth. Cultivated on Columbia agar with 5% sheep blood, 24 hours in an aerobic atmosphere enriched with 5% carbon dioxide.