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IOWA ACADEMY OF SCIENCES. 
Ceriodaphnia censors (?) Birge. 
Ceriodaphnia reticulata Jurine. 
Ceriodaphnia acanthinus n. sp. 
Simocephalus vetulus O. F. Muller. 
Scapholeberis mucronata O. F. Muller. 
Lathonura rectirostris O. F. Muller. 
Bosmina longirostris O. P. Muller. 
Eurycercus lamellatus O. P. Muller. 
Alona quadrangularus O. P. Muller. 
Pleuroxus denticulatus Birge. 
Pleuroxus procurvus Birge. 
Chydorus sphaericus O. P. Muller. 
Camptocercus rectirostris Schoedler, 
Polyphemus pediculus Linn. 
LAKE MANITOBA. 
Bosmina longirostris O. P. Muller. 
Chydorus sphtericus O. P. Muller. 
Leptodora hyaulina Lilljeborg. 
CERIODAPHNIA ACANTHINUS, N. SP. 
The body is large, round, with the valves of the shell forming a well 
developed posterior spine. The head is separated from the body by a very 
deep depression. Head is low, small, rounded in front of the eye, sinuous 
above and angled between the eye and the antennules; the lower margin is 
nearly in a line with the lower margin of the valves of the shell 
The shell is very strongly reticulated with small, very sharply-marked 
hexagonal reticulations measuring about .016 to .021 mm. across. Small 
sharp spines project from the angles of the reticulations, many at nearly 
right angles with the surface of the shell. In the possession of these spines 
this species closely resembles C. setosa, Matile. No spines were seen on 
the rounded front of the head as are usually present in C. lacustris, Birge. 
The dorsal margin of the shell is arched, curving gradually into the pos- 
terior margin. 
The posterior spine of the shell may be near the dorsal margin, or one- 
third the distance from the dorsal to the ventral margin. When the spine 
is situated low the posterior shell margin above is slightly concave. The 
spine is as well developed as in C. lacustris, Birge, and often ends in blunt 
teeth, but is not divided into two parts at the end as is sometimes the case 
in that species. The posterior margin of the shell curves gradually into 
the strongly convex ventral margin. The fornices are greatly developed, 
extending almost the width of the shell. They are almost as broad but are 
not so sharply angled as in C. lacustris, and do not end in sharp teeth. 
The antennules are short and thick, reaching to or a very little beyond 
the angle behind the eye. Setae are present toward the distal end. The 
antennae are long and rather slender; the setae reach nearly to the posterior 
margin of the shell. 
The post abdomen is of moderate size, slightly tapering toward the end 
and is armed with nine to eleven strong recurved spines of nearly equal 
size, except the first and last, which are smaller. The anal claws are long, 
