These are very odd items, being more like single cel projector slides, or film transparencies, than cards, and which measure 37 x 34 mm.
There is no set title on these, but the special albums carry the wording "Flixies Album" and from that we named the sets.
Each of the three albums took four sets, being held in by corner slots. In our British Trade Index Part II, issued in 1969, it tells us that the other sets in that album were Dog Series, Aviation Series, and British Bird Series.
Blue Cap was a brand of cheese, and had earlier (1953-1959) issued five sets of what are classed as package issues, being trimmed out from the boxes. Series A, B and C were each twelve cards in the "Farm Series" and they were designed so that the bottom of the circular box was cut off in its entirety to form the "card". However Series D ("Sports Series") and E ("Animal Series") had two small cards printed on which were designed to be cut out separately.
These sets were again twelve cards in length but the "Animal Series" seems to have ended prematurely and in the British Trade Index Part II, it was said that numbers 9 - 12 were not thought to have been issued. However these had been found by 1986, when British Trade Index Part III was issued.