Not to be confused with the 0-4-2T 3521s that ended up as 4-4-0s, these were 2-4-0Ts that ended up as 2-4-0s.  Built in 1885, the ten double framed 3511 2-4-0Ts were a tank engine version of the Stella class 2-4-0s, a part of a Dean standardisation exercise that also included the 2361 outside frame version of the Dean Goods and the 1661 0-6-0ST. All had major components in common. They were a much larger engine than the Metros with 17in by 26in cylinders and class P (Dean Goods) boilers. Originally (as shown) they carried condensing apparatus for use in the Severn Tunnel. 3501-10 were similar, but built as convertibles for the broad gauge.  The 3511 series lost tanks and gained tenders to become additional members of the Stella class in 1894/5.

This sketch was quite a challenge. I started it because I was given a couple of blueprints of weight diagrams of the class, but when I came to trace the blueprints the frames just didn't look right to me against photographs. I've decided, on *very* limited evidence, that the running plate on the drawings is a little too low, and so I lifted it and now I think it better matches photographs. 

Sketch updated 1st Feb