IOWA ACADEMY OP SCIENCES. 
163 
Pleuroxus exiguus Lilljeborg. 
Alona guttata Sars. 
Graptoleberis testudinaris var. inernis, Birge. 
This gives a total list of thirty-one species of Cladocera 
reported from the state. 
DESCRIPTION OP A NEW SPECIES— DAPHNIA HYBUS. 
The body is large, robust, with a prominent keel- shaped pro- 
jection on the dorsal margin immediately anterior to the brood 
chamber; the projection rises at a rather low angle anteriorly, 
approximately 20 to 25 degrees, but falls posteriorly at a greater 
angle, approximately 40 to 50 degrees. It is present on the 
ephippial females and also on those bearing summer eggs. The 
measurement of the projection on one specimen gave the length 
of .14 mm. and a height of .05 mm. On one specimen a 'second 
projection is present, located on the dorsal margin above the 
base of the antennae. Measurement showed its length to be 
.28 mm. and height, .09 mm. In yet another specimen the pro- 
jection above the base of the antennae is evident under the shell, 
and it would apparently have become external at the next moult. 
The dorsal margin of the shell is convex, minutely spined from 
the posterior shell spine nearly to the front of the brood cham- 
ber. In one or two specimens the spines were not observed. 
The ventral margin is strongly convex, and is armed with small 
spines about one-half the distance forward from the posterior 
shell spine; the margin is sinuous below the posterior spine, 
which is situated usually about half wmy between the median 
line of the body and the dorsal margin, but sometimes nearly 
on the median line. Spine is straight, slender, directed slightly 
upward, .77 mm. long in one specimen, and has scattering, 
feeble spinules. 
The head is broad, not helmeted, strongly arched dorsally, 
and is not separated from the body by a depression. The ven- 
tral margin of the head is slightly concave below the eye, mid- 
way between the front of the head and the end of the long beak. 
Depth of the head is about two times the length from the base 
of the antennso. 
The eye is of medium size, with few prominent crystalline 
lenses, and is situated at a distance from the front of the head, 
about equal to the diameter of the pigmented portion. Dis- 
tance of the eye from the posterior margin of the head is little 
greater than diameter of the eye. The transparent orbit 
reaches to the front of the head. Pigment fleck is small, not 
