Hubble classified galaxies as elliptical or spiral.  The elliptical galaxies are designated with E and then a number indicating the elongation of the galaxy:  En, where n = 10(a-b)/a  a = long diameter, b = short diameter.  The spiral galaxies are divided into two major types, normal and barred.  Both normal (designated with S) and barred (designated with SB) are further divided into 3 subclasses:  a = largest bulge to disk ratio, most "wound" spiral structure; through c = smallest bulge to disk ratio, least "wound" spiral structure.