Types of Galaxies  (pg. 254-255)
Spirals
      Sa                   Sb              Sc
   (large nuclei        small nuclei)
   (little gas,dust    lots of gas, dust)
     SBa                SBb            SBc    (as above, with BARS)
Ellipticals
E0  E1 E2 E3 E4 E5 E6 E7
(spherical)               (highly elliptical)
Irregulars