ENTOMOSTRACA OF MINNESOTA. 241 
pressure, but there is nevertheless greater proportional length than 
in ordinary specimens of 4. quadrangularis, and we may have to do 
with a new species. 
Accordingly we quote our original description. 
‘Form sub-quadrangular; height about once and one-half in length; 
the dorsal outline forming a regular and low curve from end of head 
to upper posterior margin; lower outline very slightly sinuate, ante- 
rior one not at all; posterior angles rounded; head nearly horizontal; 
eye of moderate size; pigment fleck considerably smaller; antennules 
rather large, with unequal sensory hairs at the end, one spine just 
above the end in front and a bunch of minute hairs near the base 
behind; antennze comparatively large, basal joint spiny, outer ramus 
with three set, two of which have thorns at their middle, also a termi- 
nal spine; inner branch with two of the terminal set thorned and the 
upper lateral sete reduced. The post-abdomen is very broad and 
short, expanded below and rounded at the end; the terminal claws 
are straightish, denticulate, and the spine at the base is also dentate; 
there is a series of heavy spines on the upper margin of the post-ab- 
domen, accompanied by a series of scales on the side. The shell is 
unornamented and fringed below with short bristles. Length 0.9 mm., 
or more. This fine species is recognized by its smooth shell, the hori- 
zontal position of the head, and the form of the post-abdomen; it be- 
longs among the largest of the genus. Lakes near Minneapolis not 
rare. 
‘‘Birge quotes A. spinifera from Wisconsin. In all probability that 
species is the younger stage of the ahove.”’ 
The American form, which we identified with Alona oblonga, was 
said to differ from A. quadrangularis in the following points: 
‘‘The greatest height of the shell is anterior to the middle; the 
lines are less evident, and all confined to the lower part of the shell, 
while the centre of the valves is marked with very minute strie; the 
pigment fleck equals the eye, and the post-abdomen is of about the 
same width throughout and hardly as round below. This and the 
preceding species have a well-marked keel on the process of the labrum, 
The size is greater, this being one of the largest and most abundant, 
as well as one of the most striking species. It, perhaps, should rank 
as a well-marked and permanent variety of the above. Length 0.9 to 
1.0mm. The abdomen of the male is narrowed at the end and lacks 
the teeth. Lakes about Minneapolis. 
“(A small form of A. quadrangularis in Lake Calhoun had the eye 
and pigment fleck equal and the terminal claw smooth. )’’ 
We are satisfied that a wide range of variation must be allowed 
for. The presence or absence of markings is unreliable. 
