1. Stellar Image. (I) (IC 4997)
2. Smooth Disk (II) (IC 2003 / IC 5217)
2a. Smooth Disk, brighter towards center. (IIa) (IC 351)
2b. Smooth Disk, uniform brightness. (IIb) (IC 2448)
2c. Smooth Disk, traces of ring structure. (IIc) (IC 972)
3. Irregular Disk (III) (NGC 7008 / NGC 1501)
3a. Irregular Disk, very irregular brightness distribution. (IIIa) (M97 / NGC 7026 / NGC 7027)
3b. Irregular Disk, traces of ring structure. (IIIb) (NGC 7048)
4. Ring Structure. (IV) (NGC 7094, NGC 6818)
5. Irregular Form, similar to a diffuse nebula. (V) (NGC 6765)
6. Anomalous Form. (VI) NGC 6302
