This is not a PCI-X connector but a PCI Universal connector (32-Bit). This connector indicates that the card should work with 3,3 Volts or 5 Volts provided by the PCI-Slot.
Check:
https://en.wikipedia.org/wiki/Conventio…:PCI_Keying.svg
The card should work anyway as Mercury bricks/ systems from Quantum3D used the PCI-X Slot on the installed Intel L440GX+ Motherboard.
I believe that this card is quite interesting since it has a black PCB (early version with four single heatsinks, Chips running at 100Mhz) but is equipped with a "newer" PCI Universal connector which was normally used on the later boards (late version, chips running at 125Mhz, large heatsink for all four chips). I assume that this is actually the reason why the "brick" which contains four cards will not work (mixed early/late).
Anyway, thank you for the pics.