XGMII interface

Dears: As in IEEE 802.3 clause 46, in 10G Ethernet, RS and PCS may use XGMII interface to inter-connect. XGMII interface is a 32-bit wide, transmit & receive data path, working on frequency of 156.25HZ. So, for transmit direction, the total transmit rate should be 32*156.25=5Gbps, how 10G works with this interface? Further, on PMA, the transmit rate become 312.5M characters per lane.. how done this number come? thanks!