ey, GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
with about ten teeth. The claws are short and curved and have one 
basal spine and fine teeth. The palp of the male antenna has two 
Sete. 
This species has been found near Madison by Birge and by Forbes 
in Lake Michigan. 
FAMILY DAPHNIDE. 
The family Daphnide contains the genera Moinadaphnia, Moina, 
Ceriodaphnia, Scapholeberis, Simocephalus and Daphnia, which include 
the commonest, as well as some of the largest, Cladocera. The genera 
may be distinguished by the following table: 
I. Head rounded, not beaked; antennules long in both sexes, shell 
not covering the end of the abdomen. 
a. Abdomen with process of abdomen to retain ova, . Moinadaphnia, 166 
b. Abdomen without the process in ordinary females, . . . Moina, 160 
II. Head rounded; antennules rather short; shell inclosing whole 
hody, Pra Ge? ec OR Riek eae Ceriodaphnia, 167 
III. Head somewhat beaked below; shell angled below or extending in 
long spines from lower angle, pigment fleck roundish, Secapholeberis, 174 
IV. Head beaked below; shell rounded below, with a blunt spine 
above; pigment fleck elongate, . . . . . . Simocephalus, 177 
V. Head beaked below; shell extending in a sharp spine at the upper y 
posterior angle; pigment fleck small, . . . . . . Daphnia, 181 
The Circulatory System of the Daphnidee. 
PLATE LI. 
In the Daphnide, and, indeed, the Cladocera in general, we meet an 
instance of great development of surfaces at the expense of solidity of 
form and compactness of organs. The whole body is composed of an 
aggregate of laminz, and the appendages all approximate more or 
less toward this fundamental modification. Thus, for example, the 
head is a leaf-like body with a laminate shield above and a pair of flat 
organs beneath. The abdomen terminates in a knife-like post-abdo- 
men, while the thorax, with its narrow form, foliaceous feet and, far 
more, the enormous development of the outer wall to inclose, more 
or less fully, the entire body, is the typical illustration of this fact. 
Necessarily this structural modification exerts a formative influence 
on the internal organs which are all more or less influenced by it; and 
this is peculiarly the case with the more external and, in general, the 
paired organs. Thus the ‘‘shell glands,”’ so called, which in Copepoda 
are generally coiled tubes, become here greatly flattened organs closely 
united with the shell. The physiological result of this modification 
is the sensitiveness to changes in the environment, which is universal 
