Old World porcupines -LRB- Hystricidae -RRB- have quills embedded in clusters , whereas in New World porcupines -LRB- Erethizontidae -RRB- single quills are interspersed with bristles , underfur , and hair .

Old World porcupines -LRB- Hystricidae -RRB- have quills in clusters , whereas in New World porcupines -LRB- Erethizontidae -RRB- single quills are mixed with bristles , underfur , and hair .
