The Bugatti Type 57 and later variants (including the famous Atlantic and Atalante) was an entirely new design by Jean Bugatti, son of founder Ettore. Type 57s were built from 1934 through 1940, with a total of 710 examples produced. Most Type 57s used a twin-cam 3,257 cc engine based on that of the Type 49 but heavily modified by Jean Bugatti. Unlike the chain-drive twin-cam engines of the Type 50 and 51, the 57's engine used gears to transmit power from the crankshaft.
Just two supercharged Type 57SC cars were built new, but most 57S owners wanted the additional power afforded by the blower. Therefore, most of the original Type 57S cars returned to Molsheim for the installation of a supercharger, pushing output from 175 hp (130 kW) to 200 hp (150 kW) and 120 mph (190 km/h). 2014 saw the unveiling of Ralph Lauren's unique $40 million version of this classic.
The Atlantic body Type 57S featured flowing coupe lines with a pronounced dorsal seam running front to back. It was based on the "Aérolithe" concept car of 1935 and styled by Jean Bugatti. Like the Type 59 Grand Prix car, the Aérolithe used Elektron (a magnesium alloy) or Duralumin (an aluminium alloy) for its body panels. Therefore, the body panels were riveted externally, creating the signature seam.
Source: Wikipedia (original)