June, 1906.] 
Key to the Order Thysanura. 
547 
DD: 
EE : Terimnal segment of antennae long, annulate. 
F: Antennae with 8 segments, abdomen with 2 tubercles. 
Gen: 2 (10) Dicyrtoma. 
FF: Antennae with 4 segments, abdomen without tubercles. 
Gen: 3 (11) Sminthurus. 
Abdomen clyindrical, longer than broad. 
Fam;6, EXTOMOBRYIDAE. 
E: Body naked or covered with hair. 
F: Antennae of 0 segments. Gen: 1 (12) Orchesella. 
FF: Antennae of 4-5 segments. 
G: 2 ocelli on either side of head. Gen: 2 (13) Sinella. 
GG: 8 ocelli on either side of head. 
H; Dorsal portion of third and fourth abdominal 
segment approximately of equal length. 
I : Central part of saltatorial organ not reach- 
ing- over the ventral sucker. 
Gen; 3 (14) Isotoma. 
II; Central part of saltatorial organ reaching 
beyond ventral sucker. 
Gen; 4 (15) Corynothrix 
HH: Dorsal portion of fourth abdominal segment 
3-4 times longer than third. 
I : Distal end of saltatorial organ curved, 
without antiapical hooks. 
Gen: 5 (16) Drepanura. 
II; Distal end of saltatorial organ simple, with 
antiapical hooks. 
J : Ocelli irregularly arranged, not in 2 
longitudinal and 4 transverse rows. 
Gen: 6 (17) Entomobrya. 
JJ; Ocelli symetrically arranged in 2 
longitudinal and 4 transverse rows. 
Gen: 7 (18) Salina. 
EE; Body covered with flat scales. 
F: Antennae of 4 segments. 
G; Distal segment of antennae annulate. 
H: Ocelli present. Gen: 8 (19) Tomocerus. 
HH; Ocelli absent. 
1 : Antennae longer than body, saltatorial 
organ with long distal segment. 
Gen: 9 (20) Tritomurus. 
II; Antennae half as long as body, saltatorial 
organ with very short distal segment. 
Gen; 10 (21) Heteromurus. 
GG: Distal segment of antennae not annulate. 
H: Ocelli absent. Gen: 11 (22) Cyphodeirus. 
HH; Ocelli present. 
1: Pronotum simple, head prominent. 
J ; Metathorax enlarged into hump. ' 
Gen: 12 (23) Campylothorax. 
JJ: Metathorax simple. 
K; Middle part of saltatorial organ 
spiny. 
Gen: 13 (24) Dicranocentrus. 
KK: Saltatorial organ smooth. 
L: Fourth abdominal segment 
almost 3 times as long as 
third. 
Gen: 14(25)Pseudosira. 
