The DEP215 is a four pin triode from Osram that has internal metalisation obscuring most of the internal construction. The advert linked above shows the horizontal box anode with two parallel filament threads within the grid.
The structure of the pinch in the round stem with the horizontal electrode supports just visible.
The Type designation is etched clearly into the dome of the envelope.
Looking up under the gettering the flat rectangular box anode can be seen.
With enhancement the grid can be seen on the right.
The balloon envelope is 46 mm in diameter and, excluding the B4 base pins, is 85 mm tall.
References: Advert & 1043. Type DEP215 was first introduced in 1927. See also1927 adverts.