This is one of the more rare rizzuto knives. It is known as the knuckle rizzy or finger groove rizzy for obvious reasons. This model measured about 8.75 inches open length. This particular example has the stronger, less glossy scales. It also does not have the the rizzuto estileto milano stamp on the blade, just stainless steel on the tang. Taken together, this example appears to be earlier.
Images courtesy of Mark Erickson of Apple Valley Knives.