This is very interesting lens, which is obviously genuine. It could be a very early version, before the series III found its standard engraving. Or, as Tim mentioned, a Petzval 6B in a plain barrel. The Petzval has a focal length of 12" and covers just full plate, whist the 6A series III has afocal length of 15.33" and covers more than 11x12". The front and rear cells on the Eurooskop III are identical.

The serial number points to this being an intermediate engraving design. It was about this time that anon. Euroskops began to be engraved with more detail about them. The only identification had been a arabic or roman numeral at one edge of the barrel.