That's a beautiful plant you have there. This is a P. subterranea, and maybe the P. culpinensis (which is now classified as synomym of P. subterranea) becouse of the longer spines.
Pieter

{{gwi:476188}}

Thank you Xerophyte, I took the wrong link.
Thank you Pieter, your mr W. verheulpen says it's not a hybrid but p subterranea. harry

OK Hablu, Willy is the big specialist here :-)