It happened Thursday at 10:43 a.m. at the Sovereign Bank branch in the GSB Building at City Line and Belmont Avenues.
Police say the man walked into the branch, handed the teller a demand note and fled with an undisclosed amount of cash.
The surveillance picture shows an African-American man with a goatee beard wearing a dark colored shirt, a brown winter cap and large black-rimmed glasses.
Anyone who recognizes the suspect or has information about the crime is asked to call Lower Merion Police at 610-649-1000.
