ENTOMOSTRACA OF MINNESOTA. 167 
with the fauna of the southern hemisphere. The species is large 
compared with Monia, being 1.68 mm. long. The head is shaped much 
as in Simocephalus, being acutely rounded in front of the eye and pro- 
vided with a distinet beak, near which the antenne are attached. The 
eye is large and the fornix evident, asin Daphnia. The antennules are 
long and slender, little narrowed apically, armed with a flagellum at 
the basal third. Antenne slender, segments narrow; apical segment 
of four-jointed ramus has in addition to the three geniculate set a 
very long spine representing the short thorn occupying that place in 
Moina, otherwise as in that genus. Body quadrangular, somewhat 
produced above at the posterior angle. Lower margin armed with 
short spines asin Daphnia. Abdomen slender, claw slightly curved 
and armed with a continuous series of small sete. A short spine in 
front of the claw. Lateral spines as in Moina, twelve or more in num- 
ber, the first being bifid. Dorsal part of abdomen with a long process 
for occluding the brood sac, also a blunt tuberosity caudad of it. The 
general habitus is like Moina, but in the form of the shell and many 
details it approaches Daphnia. The description of King’s species is 
not full enough to make specific comparison possible, but of the generic 
relationship there can be no question. The most important diagnostic 
difference —that in the formula of the antennary spines— not funda- 
mental but a mere matter of proportions. 
GENUS CERIODAPHNIA Dana. 
The genus Ceriodaphnia is the successor to Moina, which some species 
greatly resemble; the post-abdomen, however, is shorter and has a 
habitus resembling Daphnia; the antenne are smaller and the shell is 
thick and coarsely reticulated. 
Ceriodaphnia has the same general mode of life as Moina, living in 
muddy pools in late summer and bearing numerous broods which often 
greatly extend the brood cavity. The antennules are shorter but have 
a similar form; the male antennze show a transition in the various 
species from forms adapted for prehension to such as are found in 
Daphnia. The brood cavity is closed by two ridges on the abdomen 
instead of one, as in Moina, or three, as in Daphnia. 
The ephippium contains but a single ovum. In general, the form 
is oval or quadrate, angled but not spined posteriorly; head separated 
from the body by a deep depression; pigment fleck present; beak 
absent; antennules movable, rather short; antennz with the three- 
jointed ramus with five sete; first foot of the male with a hook or 
flagellum. 
