Sorting through old family photographs

Found a bunch of old photographs that my dad took on a tour of the States in the early 80's (we are from the UK). The prints are a bit smaller than a standard 4 x 6 and they have rounded corners and are more matt than a usual photo, and none of the other photos in this box are that size. Is there a name for this format? Was it only available in the US in the early 80's? They're really satisfying as a physical medium and I just want to know more about it. via /r/photography https://ift.tt/2XpW5BS