The Cossor 215P is a directly heated battery output triode from about 1927. Originally issued as the Stentor Two in 1927. The 215P had an upgrade in 1930 when the New Process valves became available. The data-sheet reflects this later version with a higher possible anode voltage.
The gettering obscures the internal structure.
The dome carries the company name, BVA logo and manufacturers codes, probably date information. The Type designation is only given on the paper label.
The balloon envelope is 41 mm in diameter, and excluding the B4 base pins is 85 mm tall.
Reference: 1043. Type 215P was first introduced in 1930.