oups! I though the title of the topic would had been enough... sorry
In the Unitrade catalogue, the #21 is described as an 1/2 cent black of the Large Queen issue.
The cat. also identified 12 major varieties for this stamp with a specific cat. number for each of them.
The following images are to show, what I think there are, 2 of these major varieties
on the same stamp :1) #21iii : white area on bun of hair, the 'chignon' variety
2) #21iv :'spur' in scroll left of H
image 1 : regular stamp
image 2 : stamp with the 2 varities
image 3 : variety #21iii
image 4 : variety #21iv




If you want to learn more on this captivating serie, go there :
http://www.canadianstampcentral.com...umber_34.htm