RRO at Mae ee Ae ee pe nat A: eo Per 
sme ae ? fa ae . 
ENTOMOSTRACA OF MINNESOTA. 213 
mm. high, while the present form measures 1.1 by 0.7 mm.) but the 
form and several details noticeably differ. The shell, as seen from the 
side, is nearly quadrangular, reminding of Lathonura, and is not 
produced into a sharp spine as in I. rosea The head is also shorter 
and is not excavated between the eye and pigment fleck. The ventral 
margin of the valves is not obviously sinuous and is spinulus as in MW. 
rosea. The antennules are straight, and not strongly curved, as fig- 
ured by Kurz, neither are they spiny in front. At the tip they bear 
the usual sensory setz and posteriorly a cluster of spines while the 
posterior margin is ornamented with several clusters of bristles dis- 
tally. The antennez seem not to differ materially from those of J. 
rosea. The post abdomen is shorter than in MM. rosea, its terminal 
claws are small, curved, deep-colored and unarmed; in the protuber- 
ance formed by the anus are closely clustered spines and bristles 
while the rest of the margin is either unarmed or furnished with a 
few minute spines. The long stylets are as usual in the genus. No 
markings were seen on the shell. Projecting into the brood-cavity 
are two leaf-like plates which seem to serve an accessory branchial 
function and contain many blood corpuscles. Details of the feet are 
wanting. The species has been but once seen, in the clear water of 
the tank supplying Albuquerque, New Mexico, accompanied by two 
species of Diaptomus and a Moina. 
M. rosea oceurs in the north, often in considerable numbers (Birge 
’91) and the present species may take its place to the southward. It 
may be admitted that it approaches Lathonura more than any other 
species of the genus. 
It is just brought to my notice that Matile describes in an appendix 
to his paper ‘‘Die Cladoceren der Umgebung von Moskau, 1891,’’ 
Macrothrix borysthenica, which is so very close to our species that we 
suspect intimate comparison will prove the two identical. The atten- 
nules in Matile’s species are shorter and the dorsal margin is less 
strongly marked. The armature of the post-abdomen is perhaps 
slightly different but our description was drawn from very large in- 
dividuals and considerable variation was observed. I therefore with- 
draw the name proposed for the present. 
Macrothrix hirsuticornis Norman and Brady. 
Norman and Brady ’67; Daday ’88; Matile ’90. 
Head separated from the thorax by a depression. Shell roundish, 
caudal angle obtuse, smooth, ventral margin gently rounded. An- 
tennules dilated toward the end, slightly curved, cephalic margin with 
five series of small seta. Post-abdomen rounded at the end, having 
distally seven sete and proximally small teeth. Length 0.55 mm. 
