June, 1906.] 
Key to the Order Thysanura. 
549 
JJ : Legs very short, nut visible from 
above. Gen: 9 (41) Brachysius. 
MH : Terminal spur present. 
1 : 2 terminal spurs. 
Gen: 10 (42) Xenylla. 
II: More than 2 terminal spurs. 
J : 3 terminal spurs. 
Gen: 11 (43) Friesae. 
JJ : 4 terminal spurs. 
Gen: 12 (44) Oudemansia. 
BB: Saltatorial organ absent. Fam.:8 APHORURIDAE. 
C: Mouth-parts nut placed cone-like under the head. 
D: Tarsus with 2 distinct claws. Gen: 1 (45) Aphorura. 
DD: Tarsus with 1 distinct claw. 
E: Post-antennal organ absent. Gen: 2 (46) Anurophorus. 
EE: Post-antennal organ present. 
F: Terminal spur present, post-antennal organs placed in 
rows. Gen: 3(47) Tullbergia. 
FF: Terminal spurs absent, post-antennal organs in circles. 
Gen; 4 (48) Anurida, 
CC : Mouth-parts appearing cone-like on under side of head. 
D: 3 ocelli on either side of head. Gen; 5 (49) Neanura. 
DD: Ocelli absent, 
E: Post-antennal organs present. Gen: 6 (50) Aphoromma. 
EE: Post-antennal organs absent. Gen: 7 (51) Tetrodontophora. 
EXPLANATION OF DRAWINGS. 
The terminology used is practically the same as in other groups of 
insects, with the exception of the sub-order, Collembola, which are 
peculiar in that they possess a ventral sucker, and saltatorial appendage. 
The followung drawings were taken from the genus, Isotoma, which is one 
of the most generalized of the entire group. 
Fig. 1. Saltatorial appendage. Fig. 2. Antenna. Fig. 3. Ventral 
view of sucker. Fig. 4. Side-view of sucker. Fig. 5. Post-antennal organ. 
Fig. 6. Left eye spot showing the ocelli. Fig. 7. Foot, 
