This is an ordinary Heliar. There a quite a lot of these 30+ cm around, having been a very popular item in Portrait Studios.
The position of the iris, and therefore the internal mounting system, varies on these. The early ones had an iris well up on the barrel, whilst the later ones had one close to the flange. In these later ones, the central lens is attached to the front assembly with a light housing.
This is the later "clean" design.
Photo 1 shows the basic structure. The middle lens housing is shown with a few thread turns on the front cell/lens hood section. Unscrewing the front section will always "bring out" the middle section at the same.
The rear section is quite traditional with quite a good purchase surface for unscrewing.
I am not sure whether the hood is removable from the front cell. Certainly, the front lens could be removed from the rear. But there is a turned brass overlap, which would make re-balsaming difficult.
As you can see, this particular lens hood as fallen twice! I have seen a number of big Heliars with broken off sections of lens hood rims. The metal used is too brittle and not suitable for the usual "brass-type" recovery operations. However, the inserted hardwood piece shown in photo 3 provided an excellent torque for unscrewing.
Note that apparently clean bare metal interior is completely covered with fine crystalline dust (photo 4) which must be an oxidation/hydration product. This metallic dust doesn't seen to migrate onto the lens surfaces, but is best removed during the operation.
I hope the pictures help.
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