Montclair was Mercury's top-of-the-line series and brand new for 1955. And within that series was the Sun Valley moved from the Monterey series - a convertible influenced hardtop that was first introduced the previous year.
Featuring a transparent, plexiglass top covering the front half of the roof, it gave a new experience in driving with much more of the outdoors entering your range of vision.
This 1955 Mercury Montclair Sun Valley in Alaska White is one of only 1,787 cars produced that year.

Tinted Plexiglass roof
The downside of the plexiglass top is that it would cause a heat buildup inside the car.

Side view
The Montclair sat slightly lower than other Mercurys giving it a more sporty look.

Two-tone interior - note the 3-tier fan-shaped gauge cluster
Power comes from a 292 cubic inch Super-Torque V8 engine (new for 1955) with a 4-barrel carburetor. This is paired with the optional Merc-O-Matic automatic transmission and bringing the purchase cost when new, up another $190. Dual exhaust was standard in Montclair.
Further options on this particular car include power steering ($108) and power brakes ($45).
Mercury made just 1,787 Montclair Sun Valley cars for the 1955 model year. They had a base price of $2,712 and were exactly the same price as the convertible. Sadly the Sun Valley wasn't to last and it was discontinued that year.
Ford made 10,000 Fairlane Crown Victoria’s and 603 had the Plexie glass roof they like the Mercury were discontinued with the 56 model. If you are a Ford fan you will see that the dashboard layout of the 55 Mercury is very simular to the 1957 Ford Fairlane .
Mercury did not have a Sun Walley for the 56 model, Ford had Skyliners for both 55 and 56 Crown Victorias, Skyliners being the Plexieglass model. Ford did have a Plexie glass model for 1954 as did Mercury for 1954 models.