Psion Series 3c
The Psion Series 3c followed on from the Psion Series 3a and predating the Series 3mx. The main differences are: a redigned case in black with a rubberised coating (that degarded into a sticky mess over time), an infrared port, and a backlight (on later models).
I have a couple of Psion 3cs which I've refurbished from quite a few spare/repairs ones from eBay. They are subject to the usual wear and tear problems with the hinges, battery compartments and screens failing often.