Depends on the thread size of your lens. And if the Petri lens is of a different design than the Ricoh, the aux lens may not give good results on the camera it was not made for. You have to remember that back when those cameras were made, it was more important in the marketing that they have a certain maximum f stop to compete with the other brands, so sometimes there was a bit of fudging in the reporting of design features. If the one lens has six elements, and the other only five, then you stand the chance that the aux lens will not be compatible with the other brand. OTOH, Petri may have made aux lenses for more than one brand, so it's a crap shoot until you try it.
Good luck, and don't spend too much money on them.
PF