2. Myron Harmon Swenk 
included. These form a compact group of allied species, includ- 
ing about one-third of the North American forms. It is the in- 
tention of the writer to subsequently treat the remaining species 
in a similar manner. 
The chief difficulty in depending on the color of the pilosity for 
specific characters lies in the tendency of the original color to 
undergo a rapid fading, so that a specimen in which the hair of 
the thorax and face was of a bright yellowish color when fresh 
will, in a short time, fade to a pale gray without a tinge of yellow; 
hence such dichotomy as “hair of face yellowish” against “hair 
of face white’ becomes utterly valueless as a distinction between 
species. And added to this is the general faded appearance of a 
species in the more arid portions of its range, even in perfectly 
fresh specimens. Thus C. armatus in Nebraska has the thoracic 
pubescence of the male always dull gray, while fresh eastern spec- 
imens have it deep ochreous gray mixed with black; the two are 
beyond all doubt conspecific, yet in the majority of tables would 
run far apart. Nor is such fading confined to the pubescence, for 
a similar variation in color is found in the nervures, which vary 
in the above mentioned species from brownish black to pale tes- 
taceous. The amount of brownish suffusion of the apical tarsal 
joints, the amount of red on the mandibles, the intensity of shade 
on the lower surface of the flagellum, the shade of color of the 
tegulae, and other characters based on the color of the integu- 
ment, all-vary so greatly in. different specimens, which have ex- 
perienced a greater or less amount of weathering, as to render 
them quite useless. The size and arrangement of the abdominal 
fasciae is another character largely used by workers in this group. 
That these possess some value when unmutilated is not ques- 
tioned, but so easily do they rub off that one must go over a large 
series of specimens before finding a perfect one, and discrimina- 
tions based on the characters of the fasciae alone would prove of 
no value in determining the great majority of specimens. The 
presence or absence of black thoracic hairs is really about the only 
character in the color of the pilosity which is of constant value 
and phyletic significance. The sculpture of the labrum is usually 
so difficult to see properly, and so variable in a series that its 
44 
