20 Transactions of the Academy of Science of St. Louis 
GENUS Folsomia Willem, 1902 
Eyes usually reduced in number or absent. Body pigment 
lacking or reduced. Mucro usually with two teeth and only 
rarely three teeth. Abdominal segments four to six are often 
ankylosed completely. Sometimes the suture on the dorsal side 
between the fourth and fifth is evident. 
Folsomia fimetaria (Linnaeus), 1758 
Figures 18-21; approximately 1-2 mm.; white and completely 
without markings; eyespots entirely absent; antennae 4-seg- 
mented, segments to each other as 4, 8, 9, 15; unguis without 
teeth and somewhat curved, unguiculus about two-thirds as long 
as the unguis, lanceolate and untoothed; hind claws larger than 
other claws without tenent hair; abdominal segments 4, 5, and 
6 without dorsal sutures ; 20-25 crenulations dorsal of the dentes; 
mucrones bidentate; a few scattered long setae over the body 
surface and more numerous small setae. 
Records: March 15, 1936, Buder Park, one mile west of 
Valley Park, Missouri, (Leslie Hubricht). 
GENUS Isotomurus Borner, 1903 
Eyes eight on each side. Unguiculus and furcula present. 
Dorsal side of the dentes crenulate; dentes long and slender. 
Mucro lamellate, four-toothed. 
Isotomurus palustris (Miiller), 1776 
Figures 22-28; length approximately 1.5-2 mm.; under parts 
and legs lighter than the upper parts; with a dark irregular 
dorsal median stripe and a somewhat lighter irregular stripe 
on each side of the body; furcula with some pigment on the 
proximal part and attached to the fifth segment; antennae 4- 
segmented and somewhat longer than the head, segments to each 
