What is the difference between PCIe slots and AGP slots?

Consider this image of the slot part of two cards, a PCIe 16x graphics card and an AGP 8x graphics card :

AGP Slot !!! BFG GeForce FX 5500 OC gpu !!! AGP Slot !!! $ · Parker Performance PCs Jawa Verified

agp slot function AGP is a superset of PCI clocked at 66 MHz, and usually benefiting from having its own exclusive bridge to the processor bus Thus he reasoned

agp expansion slot Slot agp Visitante Por Visitante 9 de outubro de 2003 em Placas-mãe