ENTOMOSTRACA OF MINNESOTA. 227 
a. Head nearly horizontal, blunt; post-abdomen prominent in the 
analerepion.. | 20) . . . Graptoleberis, 235 
b. Head depressed, acute; poeeandomen excised near the anus, 
Dunhevidia (= Crepidocercus), 236 
€. Post-abdomen more or less quadrangular, armed with one or two rows 
of small teeth on either side behind; terminal claws with one or 
two basal spines; height of posterior shell margin usually less than 
the greatest height of the shell. . . . : . Lynceus, 237 
D. Pcst-abdomen terete; greatest height of shell little jess than that of 
posterior shell margin; terminal claws very minute. : Phrixura, 
E. Greatest height of shell more than double that of the posterior margin. 
a. Eye and first foot normal. . . . . . Chydorus, 260 
b. First foot with a claw which extends tend shell. Anchistropus, 264 
c. Eye absent, only the pigment spot used for vision. . Monospilus, 264 
(Not noticed in the key. . Alona, 238; Alonella, 249; Pleuroxus, 253 ) 
SERIES A.—This section is proposed for the old genera Camptocercus, Acroperus, 
and Alonopsis, which seem to form a natural group though passing into Alona. 
GENUS CAMPTOCERCUS (> Camptocercus Baird). 
This easily recognizable genus contains two groups, each with sev- 
eral nominal species, which are distinguished mainly by the width of 
the post-abdomen. In both the shell is elongated, more or less quad- 
rangular, longitudinally striate, armed behind with one to four minute 
teeth. ‘The head and back are keeled and the former strongly arched. 
The antennules rarely extend beyond the beak and are commonly 
curved laterally. The eye is proportionately small. The post-abdo- 
men is long and furnished with a lateral row of scales. The terminal 
claws have a single basal spine and are serrate. There is an ephip- 
pium, and the male opening is in front of the terminal claws. 
SUB-GENUS ACROPERUS Baird. 
Post-abdomen broad, margins parallel; anal teeth very minute, 
lateral scales large and usurping their place. Antenne with eight 
setae (39°). Three species are described, one of which is very abund- 
ant in Minnesota. 
*Acroperus leucocephalus Koch. 
PLATES LX], Fie. 5; LXII, Fie. 9 
Lynceus leucocephalus—Koch, Fischer. 
Acroperus harpe—Baird. 
Acroperus sp.—Herrick. 
Acroperus striatus—Jurine, M. Edwards, Lievin, Lilljeborg, Leydig, etc., seems to 
belong here, but I am able to add nothing to the elucidation of the puzzle. 
Body rounded above, angled behind; head moderately arched and 
carinated. Lower margin of the shell pectinate, terminating in two 
15 
