If it's a pair of cemented doublets it's not a Petzval. The Petzvals have an uncemented rear pair.
In about 99.5% of the cases, an unknown old lens with two cemented doublets will be a Rapid Rectilinear.
The last half percent are "nameless rectilinear" - a precursor of the RR but with the positive element on the outside and negative on the inside - one of the very few historical lens types that doesn't have a name. It's so rare that most have never seen one, as it was only made for a year or two (world wide) before the far superior RR took over completely.
By pure coincidence I happen to have one here somewhere, and I well understand why that construction disappeared without a trace the moment the RR/Aplanat was introduced.
A third possibility is a 2+2 form of Protar, but these were prestige products and will invariably be named as "Anastigmat" or "Protar".