The Jesuit cassock went the way of Jesuit adherence to orthodoxy around 1970. When it still existed, it was a buttonless cassock with a relatively thin sash that was of tough material that was wound around the mid-section several times and tied in a special way that I can't describe in writing. The collar had no square notch as does a Roman collar. It was closed in front by two fasteners and the white collar simply went around the whole neck in a manner similar to the type of collar that a Brother might wear. In fact, there was no difference between the cassock of the Jesuit priest or brother.
Up until the late 40s there was also a large rosary on the sash/belt. That went first, then the rest.
I know all this because I was a friend of several Scholastics at Fordham, some of whom wore their cassocks until around 1970, as I indicated. Anyone who wore a cassock after that was in a wheelchair or was acting the part of a ecclesiastical dandy and was the subject of jokes.