This Cintel GS16 photocell has a large curved photocathode and a rectangular wire anode in front of the cathode.
This type of photocell is operated with a positive bias of several tens of Volts to the anode and a high value series resistor. The output voltage is taken by a high impedance amplifier from across the resistor. The photo-current is only a few µAmps at most.
The side view of the electrode assembly shows the anode as a rectangular wire loop.
The face view shows the curved cathode as a rectangular plate.
The wide glass tube envelope is 26 mm in diameter and, excluding the B4 base pins, is 56 mm tall.