THE MORPHOLOGY OF THE FRONTAL APPENDAGE 
OF THE MALE IN THE PHYLLOPOD CRUSTACEAN 
THAMNOCEPHALUS PLATYURUS PACKARD 
ARTHUR T. EVANS 
NINE FIGURES 
INTRODUCTION 
In 1874 Dr. L. Watson collected near Ellis, Kansas, a singular 
Phyllopod with a peculiar frontal appendage on the head of the 
male, belonging to the family Branchiopodidae. These and 
other specimens collected by Doctor Watson were forwarded 
to Prof. A. 8. Packard, who described (’77) this particular 
species as Thamnocephalus platyurus. Since that date only 
two collections of the species have been recorded, one by Cockerell 
in 1912 from Montelair, Colorado, and one by Pearse in 1912 
from La Junta, Colorado. The material studied by the writer 
was obtained by Dr. Max M. Ellis at St. Vrain, Colorado, on 
May 31, 1912. 
Thamnocephalus platyurus is an inhabitant of the stagnant 
plains-pools of western Kansas and eastern Colorado. These 
pools are usually very muddy and distinctly alkaline, except 
immediately after a heavy rain. Since the pools are not perma- 
nent-and are formed entirely by the collection of surface water, 
they are subject to a rapid concentration by evaporation. They 
appear in early spring, dry up during the summer, and again 
appear with the rains of autumn. The specimens taken at Mont- 
clair were found in a pool about 15 feet in diameter, the water 
area of which had been reduced to about 9 feet by evaporation. 
This pool varied from a few inches to about 8 feet in depth. 
About the shore was rubbish and various plains plants, as well 
as an incrustation of alkali. The specimens studied by the 
writer were collected in a pool filling the bottom of a ‘draw’ 
about 40 feet long and 3 or 4 feet deep near its center. The 
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