CRAYFISHES OF NEBRASKA AND EASTERN COLORADO 
97 
evidence, added to that of Ortmann, Harris, and others, that the chimney is no part 
of the economy of the crayfish burrow but is the easiest method of disposing of the 
material excavated. In this case the material was brought to the surface of the 
tunnel and thrown over the edge, to be swept away by the current. The openings 
of the burrows were difficult to find, as they were beneath the outthrust roots of 
shrubs and trees and were often 3 feet above the water level. Young of this species 
were found in the water throughout the period of 10 days spent in that vicinity in 
late August, and none in the burrows, each of which was occupied by a single adult. 
This species has been found in many types of soil, such as clay, sandy loam, black 
loam, gravel, and shaly limestone, but always on the banks of clear streams and 
never in ponds. 
A variety of Cambarus immunis ( C . immunis spinirostris ) is found throughout 
eastern Nebraska. It is primarily an inhabitant of small, sluggish streams, making 
a characteristic well in the banks of the stream. In one pond, however, near such 
a stream, I repeatedly found mature crayfishes of this variety in the open water 
and none were taken from burrows on the banks of this pond. 
Cambarus virilis occurs in the swift, sandy-bottomed streams, the most constant 
locality known to the writer being the Blue River at Milford, Nebr. I have not 
failed to find a few on each trip in the swift, well-oxygenated water just below the 
milldam. C. immunis is found in great numbers in adjoining mud flats, but the 
two species have not been found to overlap. C. virilis and C. diogenes were both 
found in the same area in a creek near Grand Island, Nebr. — C. diogenes in one of its 
characteristic wells and C. virilis in the creek bed. C. virili does not dig a well. 
Cambarus propinguus is an inhabitant of the more quiet places in small creeks, 
sometimes making a shallow excavation, more often hiding through the day in old 
cans or beneath rocks in the stream bed. It has been found in the same stream 
with C. diogenes, but in the more quiet, deeper sections, and it. is not a chimney 
builder. 
Cambarus argillicola has been found in Nebraska, but the data are not ex- 
tensive enough to determine any specific physical character of its environment. 
The specimens were found at different times in a single meadow pond, within 
shallow excavations or beneath stones. 
It would appear that in this group of crayfishes studied the reaction of the 
physical environment is well defined, and that the animals differ in physiological 
as well as taxomomic characters. 
The breeding habits of the group are well summarized by Andrews (1904 and 
1906), who made a careful study of the copulation, egg laying, and development of 
Cambarus a finis. The difference in times of ovulation and freedom of the young 
from the egg capsules is very interesting. My own observations are limited to a 
study of C. immunis and C. diogenes, and represent a careful investigation of their 
life history through two consecutive seasons. 
Two “berried” females of Cambarus immunis, 70 and 110 millimeters long, 
were found in burrows in a pond near Lincoln on April 25. These were taken to the 
laboratory, where the young of each hatched within 10 days. Both of the adults 
