ENTOMOSTRACA OF MINNESOTA. 189 
* Daphnia minnehaha Herrick. 
PLATES XLIX, Fias. 1, 2a; L, Fies. 1, 2; LII, Fries. 1-3. 
Herrick ’84; Birge ’91. 
This species, which occurs in small pools in autumn (affluents of 
Minnehaha creek, ete.,) closely corresponds apparently to Sars’ 
Daphnia carinata but differs in numerous points. It, in fact, is more 
nearly related to D. pulex than the group under which that species 
is placed. 
The form is oval, arched above, narrowed posteriorly, terminating 
in a rather short spine which curves lightly upwards. In males and 
young females the spine springs from the upper angle, but in old 
females having many summer eggs the spine is nearly median. The 
head is depressed, strongly arched and keeled slightly above the eye, 
which occupies the extreme end of the forehead. The keel of the head 
extends into a slight angle over the heart and continues down the back. 
In young females and in males the slight angle is replaced by a strong 
knife-like projection which extends into from one to four sharp teeth, 
the anterior tooth being directed forward. The males, in particular, 
have this feature emphasized. D. longispina has a somewhat similar 
projection, but the more nearly related forms seem not to show this 
peculiarity. The beak is slightly curved and the lower margin of the 
head is slightly sinuate. The shell has the usual square reticulations 
and is usually very transparent but in peaty waters becomes brownish. 
The size is small but variable; 1.8 mm. is a common measurement. 
The post-abdomen is narrow, the claws are armed with four or more 
teeth and a series of lateral bristles. The anal spines are eleven or 
more in full grown females and decrease only moderately upward. 
The processes of the abdomen are distinct. The males are smaller and 
Strongly carinated above and of the same form as young females. The 
antennules are rather long, with a short lateral and a long terminal 
flagellum, which latter is more than twice the length of sensory set 
which are partially lateral. The first foot has a strong claw and a 
long flagellum, while the second feet have a small spiny hook. ‘There 
is a Single abdominal process which is not hairy as in D. pulex. 
The following measurements may be added: Female—Length 
1.44 mm., spine 0.33 mm., head 0.26 mm., depth of head 0.46 mm. 
Male—Length 1.0 mm., spine 0.17 mm., head 0.20 mm., depth of head 
0.31 mm., length of flagellum of first foot 0.55 mm. Ephippial female 
—Length 1.64 mm., spine 0.20 mm., head 0.35 mm., depth of head 0.8 
mm., greatest depth of shell 0.94 mm. 
The ephippial females appear in July in the vicinity of Minneapo- 
lis, and at that time it is rare to find a female with the toothed crest 
developed. D. dentifera Forbes is closely related but has smooth claws. 
