Commuter bus from Silver Spring area to Baltimore? (buses, trains)

[Canuck2008]

Does anyone know if there's a commuter bus that runs from Silver Spring (or anywhere in Montgomery County) to Baltimore in the morning, and return at end of business day?

All I can find at the moment are MARC trains (running from Greenbelt/Union) and commuter buses that go the opposite way (from Columbia, MD to DC).

Ultimately, would like to avoid driving that commute on a daily basis.

Thanks for your help!