Indeed, this is a pair of P. ritsemai. I have recently examined the type pair of P. inermis from Stockholm museum and this is a different species with a stronger punctuation on elytra. The type pair is the only pair of inermis I know currently. So, my previous determination of P. inermis from Sabah should be wrong and must be corrected. I'm sorry for this inconvenience.
In my opinion, my presentation of discrepancies between inermis and ritsemai is consistent with the logic. Or explain me why an armed (tibiae spiny) species should be named "inermis" ?? I will try to find the original description of this species (Aurivillius,1910) and the one of P. aurivillii (Lameere, 1903).