Complex sentence: In philately, Burd specialised in early Great Britain, particularly pre-adhesive material, and was thought to possess 8000 Penny Blacks which were later sold by Charles Nissen.
Split into simpler sentences: In philately, Burd specialised in early Great Britain, particularly pre-adhesive material. He was an early student of plating and was thought to possess 8000 Penny Blacks which were later sold by Charles Nissen.