The key mainly requires you to look carefully at the paranota (singular paranotum), which are lateral extensions of the tergites (p in image at right).
 
You should also look carefully at the tiny spiracles, through which a millipede breathes. On most segments there are two spiracles on each side, opening just above the leg bases (s in image at right).
 
Finally, pay attention to the ozopores. These are openings to the chemical defence glands. In Polydesmida they open on the side of the body, one per segment, and usually on segments 5, 7, 9, 10, 12, 13, and 15-18 (H+19) or 15-19 (H+20). This is called the 'normal pore formula'. The size, shape, position and number of the ozopores can vary from genus to genus.
 
Note: For cave-dwelling H+20 millipedes from Ida Bay and Precipitous Bluff, go straight to the Atalopharetra page.

1a. Paranota broad and obvious;
                go to 2

1b. Paranota greatly reduced or absent;
                go to 10 in part 2 of the key

2a. Rear corner of paranotum clearly projecting backwards (left image);
                go to 3
 
2b. Rear corner of paranotum square or slightly rounded (right image);
                go to 6

3a. Prominent long seta arising near rear corner of paranotum;
                go to 4
 
3b. No such seta;
                go to 5

4a. Spiracles large, seemingly swollen (except Dasystigma tyleri, q.v.) adult 20-25 mm long, pale brown or chestnut brown;
                Dasystigma spp.
 
4b. Spiracles large, seemingly swollen, close together; adult >30 mm long, red-brown or purplish-brown, NE only;
                Tasmanopeltis grandis

4c. Spiracles inconspicuous, not seemingly swollen, not close together;
                Lissodesmus spp.

5a. Adults at least 15 mm long, purplish-brown; tergites flat; found in bush areas;
                Tasmanodesmus hardyi
 
5b. Adults no more than 10 mm long, pale brown; tergites with large, parallel swellings; mainly gardens;
                Brachydesmus superus

6a. Second tergite greatly expanded laterally (see image at right), tergites covered with numerous tiny bumps, adults 5-6 mm long;
                Asphalidesmus spp.
 
6b. Second tergite not greatly expanded, tergites not covered with numerous tiny bumps;
                go to 7

7a. Tergites in adults smooth, sometimes with 3 tranverse rows of low, round swellings; adults generally with reddish pigmentation;
                Tasmaniosoma and the ER group
 
7b. Tergites in adults with 3 tranverse rows of small setae; sometimes coloured but never reddish;
                go to 8

8a. Body usually well-pigmented (various colours); males with gonopods with large, rearwards-projecting 'flange' (see image at right);
                Atrophotergum spp.
 
8b. Body white or faintly pigmented; mainly tiny species 4-6 mm long as adults;
                Go to 9

9a. Males with long gonopods jointed in middle (see image at right);
                Ginglymodesmus spp.
 
9b. Gonopods without joint in middle
                F, S and T miscellany;