“(ea 
ENTOMOSTRACA OF MINNESOTA. TG 
S. cornuta from America is one of the most important supports of the 
specific independence of the two forms. All the species delight in 
disporting themselves near the surface in sunny weather. 
GENUS SIMOCEPHALUS. 
Although a very well circumscribed group, this genus passes into 
the next rather directly by means of S. macrothroides. The connection 
on the other hand seems to be by the way of Scapholeberis, though 
there is a rather broad separation between even Scapholeberis angulata 
and any known Simocephalus. The enlarged spines near the angle 
of the shell and the form of the antennules as well as some other 
points, show a transition through that species toward the present 
genus. The general form is quadrate with the lower posterior 
margin sinuate; in young specimens the shell is nearly a perfect rect- 
angle. The upper margin is produced more or less at the point of © 
union with the free posterior margin, and the shell is either arched 
or very abruptly angled above the prominence in old females. The 
head is produced into a projection at the eye, while the beak proper 
is between the anterior margins of the valves; the pigment fleck is 
rather large and variously shaped. The fornices are larger than in 
Scapholeberis and extend to the front of the head over the eyes; the an- 
tennules have a lateral flagellum which is large and lance-shaped. 
The post-abdomen varies very little in shape; it is truncate and exca- 
vated below and very broad. The anal teeth are few, large, curved, 
pectinate; the claws are straightish and pectinate or spined; the 
labrum is shaped as in Daphnia; the anterior part of the stomach has 
the usual ceca. 
The members of this genus are among the most abundant and con- 
Spicuous of the family and are more persistent during the changing 
Seasons than any other form. S. vetulus, the commonest species, stands 
in the centre of the genus, while two extremes are expressed by the 
other members of the group. 
The winter or sexually produced eggs are lodged in an ephippium 
or saddle-like modification of the shell, which is finely reticulate; while 
the shell is usually marked by fine anastamosing lines which, in some 
species, show clearly their derivation from a rather fine hexagonal 
marking. 
The sexual periods, when males are produced, occur in autumn and 
spring. The males have few distinguishing characteristics, the form 
being that of the young female. 
Theopening of the vasa deferentia is back of the anus, hence these 
ducts cross the course of the intestine. They have ejaculatory muscles 
