The Scotti Model X (the X standing for the 10th year of the Italian Fascist era, or 1932) was one of several semiauto rifles tested by the Italian military during the late 1920s and early 1930s. The Scotti entry into these competitions was chambered for the 6.5mm Carcano cartridge and used standard 6-round clips, identical to the Carcano bolt action rifles. It also used sights basically identical to Carcano rifle sights. Where it was rather unusual was its open-bolt action, a system typically found in machine guns.
Open bolt means that when the rifle is ready to fire, the bolt is locked all the way back. Upon pulling the trigger, the bolt moves forward, picking up a cartridge, chambering it, firing it by means of a fixed firing pin, and then extracting and ejecting the spent case and locking open again, ready for another shot. This system can be used with either locked or blowback actions, and the Scotti X uses a two-lug rotating bolt to lock during firing.
In total, just about 250 Scotti Model X rifles were manufactured, and the never progressed past initial field trials. A few later models were made in very small numbers as late as 1936, but these also failed to gain any acceptance. I made some slow motion videos of this rifle a little while back, and finally took the time to do a complete video on it, including disassembly: