212 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
*Macrothrix laticornis Jurine. 
PLATES LIV, Fias. 9-12; LVI, Fias. 8, 9. 
Jurine ’20; Baird 750; Fischer ’52 (Daphnia curvirostris); Lilljeborg 153; Schoedler 
58; Leydig ’60; Norman and Brady ’67; P. E. Mueller ’68; Lund ’70-’71; Fric 
1721; Kurz ’74; Herrick ’84; Birge ‘91. 
This ubiquitous species was first reported in America by Birge 
though it had been encountered by the writer in several instances. 
It is recorded at Madison, Wis., Minneapolis, Minn., where it is not 
rare, and in Albuquerque, New Mexico. 
The body is compactly oval, with a curved or subangular lower 
margin which is armed with spines which project in three planes, thus 
producing three series; dorsal margin convexly arched, crenulate or 
subdentate. Head short, produced ventro-cephalad to form a blunt 
beak from which the antennules are suspended. Eye of moderate size; 
pigment fleck large; quadrate. Antennules short, greatly expanded 
at the tip, provided with the usual sensory sete and flagella and a 
cluster of spines at their bases, also a second cluster upon a special 
protuberance posteriorly. Upon the anterior margin are series of 
bristles and this margin is serrate. The antenne are strong, hairy, 
and armed as usual in the genus. The feet are sufficiently represented 
in the figures. The post-abdomen is short, with very small terminal 
claws, in front of which are several bristles not previously noticed; 
about the anus are several bristles, and a series of short teeth orna- 
ments the dorsal margin. The whole shell is hexagonally reticulate 
except along the dorson where the slight crest modifies the markings. 
Length 4.7 to 6.0 mm. Birge found this form only rarely and then 
singly. Fric speaks of it as loving the bottom and occurring singly. 
We have frequently found it in Minneapolis and abundantly in New 
Mexico. 
As the type of the genus, it appropriately occupies a conservative 
position, as shown by broad tip of the antennules, a feature exhibited 
by embryos and young of other species. 
*Macrothrix nova-mexicana sp. n. 
PLATE LIX, Fias. 3-5. 
Testa corporis suboblongata, levis, postice non angulata, marginalibus ventralibus 
eequaliter rotundatus fere rectus, ciliatas gerentibus. Oculus magnus; macula cere- 
bralis parva sed manifesta. Antenne fere rects, ad apicem versus paulum dilatatx, 
postice ciliate. Antenne 2-di paris ille M. rosea similes. Cauda brevis, apice 
rotundato, super anum sinuata, ad apicem versus densa ciliata, margine cetero seribus 
setarum minimarum armato sive inermis. Longit 1.1 mm. 
As compared with M. rosea, its nearest ally, this form is not only 
considerably larger (the largest figures being 0.9 mm. in length by 0.6 
