Answer
On an MX Series router, 48 Layer 2 circuits can be terminated into a single VRF, per each tunnel PIC.
In Junos OS, <password> Layer 2 circuits can be terminated into VPLS by using logical tunnel (lt) interfaces. In Junos OS 9.2 Release and later, this can also be done without a tunnel PIC by using mesh groups.
For more information, click Layer 2 VPNs and VPLS Feature Guide.