50 Bulletin Wisconsin Natural History Society. [Vol. 10, Nos. 1 & 2. 
Oregon; it also occurs in Southern Canada. In the southern parts 
of Minnesota, Wisconsin and Michigan, in the northern parts of 
Illinois and Indiana, and in Iowa it is excessively abundant. It is 
also plentiful in many of the shallower lakes of Northern Wiscon¬ 
sin and Minnesota. Adams (’09) reports it from Isle Royale, 
Lake Superior, and Weckel (To) extends its range to Lake Titi¬ 
caca, Peru, where it was taken abundantly “underneath small 
rocks along the shore of Isle Planca (near Puno).” 
This species is a littoral form and is seldom found where the 
water is more than eight feet deep. As far as I am aware it is 
strictly a fresh water form, and is found in great abundance in 
lakes and ponds which retain their water throughout the year and 
which have a bottom of muck and a dense growth of vegetation, 
especially ceratophyllum and algae. Hyalellce do not take well to 
areas where the bottom is sandy, the individuals here being few in 
number.* 
Hyalellce are frequently found in rivers and creeks, if the 
temperature of the water is not too low nor the current too swift; 
sluggish, muddy streams, with vegetative growth are quite certain 
to contain them in abundance. Near Monroe, Wisconsin, in a 
little rivulet fed largely by springs, where the water was con¬ 
stantly very cold, and where there was apparently nothing favor¬ 
able to their welfare, I found Hyalellce very abundant; a species of 
Gammarus was here present in considerable numbers in the same 
habitat with them. Many such streams in various parts of Wis¬ 
consin have been examined and although Hyalellce are usually 
present in small numbers L such a habitat, it is the exception when 
they are abundant. 
COLOR. 
Hyalella knickerbockeri is a most variable species in regard to 
color. Not only are varying shades of the same color found, but 
an entirely different color and a different arrangement of pig¬ 
ment are met with in each individual to such an extent that it is 
• Shelford (1911) in his studies of ponds at the head of Lake Michigan 
found Hyalella! more common in the new ponds than in the old 
ones; in other words, he found them negatively associated with 
muck, humus and vegetation. This is directly contrary to my 
observations, and is also directly contrary to what we might 
expect from our knowledge of the behavior of Hyalellcea., they 
being decidedly negatively phototatic and positively thigmotactlc. 
But it is a curious fact that nearly all specimens taken in such a 
habitat average unusually large. 
