This small photocell has an interesting electrode structure. It may be that the cathode is ribbed for greater surface area. The anode appears to be the small disc visible at the bottom of the shielding window.
There is no Type designation on this photocell so SE has been used. Se is the element Selenium just as Te is Telurium and Au is Gold.
Rob Coleman writes: Te/Au is an alloy of gold with tellurium. This will be very 'stretchy' like chewing gum, due to the telurium, because gold is extremely soft and lacks strength. Selenium is a dark grey powder very similar to sulphur and famous for its light sensitive and semiconductor properties. Telurium was alloyed with lead to produce a very 'stretchy' alloy for pencil time fuses used in military explosive devices. A strip or wire of this alloy was put under tension and took hours to stretch.
The wide glass tube envelope is 26 mm in diameter and, excluding the B4 base pins, is 60 mm tall.
Updated July 03, 2014.