Original: Old World porcupines (Hystricidae) have quills embedded in clusters, whereas in New World porcupines (Erethizontidae), single quills are interspersed with bristles, underfur, and hair.
Simplified: Old World porcupines (Hystricidae) have quills in clusters, whereas in New World porcupines (Erethizontidae) single quills are mixed with bristles, underfur, and hair.