This is one of those "Gosh I didn't expect to get, or even see, one of them!" helmets.
As you know, Professor, the Swiss bought loads of ex-British DR and armoured troops helmets after WW2, and with various modifications used them for many years, including their own rather more highly-engineered copies (immediately identifiable by having a machine-turned rim rather than the applied rim edging of the original British helmets). This is an ex-British shell - a DR I believe, though I willing to be shown the error of my thinking - with the same liner and chinstrap rig that was used in later Swiss products up to and including the M48/62. What's more surprising about it is that it has had two very Swiss M18-type vent holes plugged into the top rear. If I understand it correctly this was done with comparatively few of these refurbished helmets.
There are a lot of rivets, some barely visible. On each side there are five functional rivets holding elements of the chinstrap and liner, and two blind, presumably leftovers from its previous incarnation.
Worth looking twice at the extraordinary paint finish too - scaling off in places but very thick and rough, looks like at least two or three coats of Swiss shadow-black on there.
The excellent - but in this case slightly confusing - WWH page has lots more information on the genuinely amazing variety of things the Swiss did with these helmets - .: World War Helmets - Casque Modèle 48 :. . And don't take them for granted either - lots were sold/donated/smuggled to the warring factions during the Yugoslav wars of the 1990s, and all these types have become scarily uncommon. Not that *I* want to encourage people to start buying them, you understand. Just you lot all stick to inflating the prices of TR helmets and British CD 'lids' - that's fine by me!