from an E.L. Ahrons sketch, this is No 342 in original or at least very early form. It was built in 1856 by Beyer, Peacock for the Commissioners of Chester General Station, which was jointly owned by the GR, the LNWR and the Birkenhead railway, and was bought by the GWR in 1865.

In this form it was really a slightly earlier version of Nos 91 and 92, also from Beyer, Peacock. In 1881 it was altered into an 0-4-0ST of much the same form as its cousins. The rebuilt locomotive looked substantially similar to nos. 91 and 92 as discussed elsewhere in this blog.  In 0-4-0ST form the locomotive was in service until 1931.

I wonder what the rationale for the conversion was. They would up rather heavy on the trailing wheels, as noted under No 92. I suppose it may have been a fixed wheelbase rather than a trailing truck of some kind, so they would have been a lot more flexible round sharply curved sidings as 0-4-0STs.