The “cross crosslet” is found as early as c.1280, in the arms of the Earls of Warwick [ANA2 408]. In medieval times, the cross crosslet (so blazoned) could be drawn either as shown, or in the form now termed the cross bottony; the two were considered equivalent emblazons, only artistically different. They are so considered in Society heraldry as well.
A field semy of crosses crosslet may be termed “crusily” or “crusilly”.
William Bekwith bears: Argent, in cross five crosses crosslet sable.
Thomas Langland bears: Per pale argent and sable, a cross crosslet counterchanged.
Griffin Crosthwait bears: Vert crusilly argent.