This is a very nice Darlot petzval. The focal length is approximately 9", f3.8, and it has an image circle of around 9". The glass is in good shape, the barrel has a nice patina, and the image is very nice on the ground glass.
The only problem I know of is that one of the focus knob screws are missing (see 3rd photo).
The engraving says 'Darlot Paris', and also 'BF & Co'. Theoretically, it could fit on a 4x4 board but it would be a tight fit. It is slightly less than 3" diameter at the threads. No flange is included.
The focal length and image circle would make it good for 8x10 portraits and anything smaller than that for landscape and portraits. On 8x10 at infinity, it will probably darken the corners some.
Price: $310 shipped & insured in the USA; Paypal and USPS money orders ok. Please email or PM if you have questions or want it. If you post here, I may not see it. $$ to APUG if sold here