18 ILLiIno1is NATURAL History SuRvVEY BULLETIN 
genital structures, (3) biology, (4) modifi- 
cations of the thorax. 
The position and height of the tree 
branches indicate the evolutionary relation- 
ships of the subfamilies, while the width of 
the branches indicates the relative number 
of species. For instance the Mirinae are 
highly developed structurally but very old 
and decadent in number of species; the 
genera and species are few in number but 
most of them are very widely distributed. 
The host plants of the Mirinae are con- 
fined to the grasses and sedges, families that 
are among the oldest and most widely dis- 
tributed plant groups. On the other hand 
the Capsinae are more recent in develop- 
ment, structurally more specialized with 
arolia and genital structures highly devel- 
oped; the species are very abundant, often 
limited in distribution, and for host plants 
utilize all the more recent plant families. 
Species of the subfamily Orthotylinae resem- 
ble the Phylinae most by absence of the 
thoracic collar, but the erect incurved arolia 
come nearest in form to the Capsinae; the 
genital claspers are highly modified and 
specialized. 
Present Holders of Material: Symbols 
If not otherwise noted the material listed 
in this paper belongs to the Illinois Natural 
History Survey. Material in the collections 
of other institutions or individuals is so 
designated by the use of the following sym- 
bols. 
FM—Field Museum of Natural History, 
Chicago; UE 
KC—Knight Collection, Iowa State Col- 
lege, Ames, lowa. 
u1i—University of Illinois, Urbana, Ill. 
USNM—United States National Museum, 
Washington, D. C. 
Measurements and Records 
Measurements given in this paper, e.g., 
“length 5.80, width 2.48,” are uniformly in 
Vol. 22ers 
millimeters. ‘These are standard with other 
literature on insect taxonomy. 
In any previously described species in 
which more than 10 Illinois records are 
available, the places are listed and the dates 
summarized. 
Tarsal Claw Key Characters 
The student wishing to identify Miridae 
should acquaint himself with the structures 
of the tarsal claws. These claws are used 
in identifying most of our forms to sub- 
family and sometimes to genus. It is highly 
desirable that the student examine a selec- 
tion of different kinds of mirids to acquaint 
himself with the various conditions of the 
arolia and pseudarolia on the tarsal claws. 
The claws are best examined at high 
magnifications against a dark background. 
If possible, it is well to examine them with 
both compound microscope and stereoscopic 
binocular. 
The tarsal claws are situated at the 
extreme end of the third tarsal segment, 
fig. 23. The simplest type is shown in fig. 
24, which has a pair of hairlike arolia aris- 
ing from the area between the base of the 
claws. In some groups, these arolia are 
membranous and thickened; in such cases, 
they are either convergent at apex, fig. 25, 
or divergent at apex, fig. 26, 9ihecestwo 
membranous types are generaly readily visi- 
ble without any doubt as to their structure. 
In other groups are cushionlike or flaplike 
membranous areas called pseudarolia at- 
tached to the claw itself. These may be very 
small; they may be present in instances 
where the arolia are either hairlike or mem- 
branous. In Illinois species, they are never 
large if the arolia are membranous. Among 
the species in which the arolia are hairlike, 
these pseudarolia are often quite large. Fig. 
27 shows an example in which the pseu- 
darolia are large and joined to the claw over 
a large surface; figs. 28 and 29 illustrate an 
example in which the pseudarolia are flap- 
like and attached to the claw only at its base. 
