I am cleaning the glass of a B & L 18in petzval projection lens. I think it's an F8.
When disassembling the rear element I find the flint and the crown.
Flint inside - Crown outside. It looks like the "original" configuration of a petzval.
Between the flint and the crown there is no spacer ring, they are mounted one on top of the other and they seem to fit correctly.

The question is:

1.- Are they mounted in this way or is there a missing spacer ring between them ???.
2.- In this lens, the configuration - flint inside / crown outside - is correct ???

Thanks in advance...