This exhibit is another Atlantic and Pacific Co. Electron Relay. This has a different anode design that is usually known as 'Short and Dull'. Unlike the 'Short and Shiny' (here) this design has the anode supported in two places.
The base cap has the Marconi logo but there are no markings on the glass to indicate the Type designation.
Thanks to Joe Gruber for sending the images.
The balloon envelope is 44 mm in diameter and, excluding the UV base pins, is 104 mm tall.
Reference: Joe Gruber.
Updated August 04, 2020. shape:balloon construction:pinch type:triode age:pre.1920 base:uv pins:4 pin:1.g1 pin:2.f pin:3.f pin:4.a