Anther is a bilobed or a dithecous structure with two lobes or two theca. Each theca have two microsporangia, so, this means that each lobe of the anther has two microsporangia. Therefore, overall there are four microsporangia in an anther (two in each lobe).
The anther is a tertragonal structure or a four sided structure with one microsporangia at each corner. So, an anther has two theca and four microsporangia.