Below is from the Arnold V specs:
ROM CARTRIDGE: 2 pcs 2 x 9 way 2.5mm pitch sockets. 1a A10 2a A2 1b +5V 2b +5V 3a *CE 4a A1 3b CLK 4b CA18 5a D7 6a A0 5b CA16 6b CA17 7a D6 8a D0 7b CA15 8b CA14 9a D5 10a D1 9b A12 10b A13 11a D4 12a D2 11b A7 12b A8 13a D3 14a SIN 13b A9 14b A9 15a CCLR 16a GND 15b A5 16b A11 17a GND 18a GND 17b A4 18b A3
however, that seems to be nonsense... or maybe an internal connector?
As seen on the photos at GX4000_cartridge, the cartridges have 2x18 pins - not 2x2x9 pins.