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216 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
*Lathonura rectirostris O. F. Miiller. 
PLATE LVII. 
Koch ’35-’41 (Pasithea rectirostris); Zaddach 744 (Daphnia brachyura); Lievin 748 
(Daphnia bracbyura); Fischer ’52 (Daphnia mystacina); Liljeborg ’53; Leydig 
760 (Pasithea rectirostris); Norman and Brady ’67; P. E. Mueller ’68; Schoedler 
’58 (spinosa); Birge ’78; Gruber and Weismann ’80 (Pasithea rectirostris); 
Herrick ’82. 
The only species of the genus is distributed probably over the entire 
northern temperate zone. It has been found in America at Cambridge, 
Mass., and in the vicinity of Minneapolis, at both of which places it 
is very rare. 
The form is a rather quadrangular oval, the head being strongly 
arched to the beak which is much farther posterior than in Macrothria, 
in this respect resembling the Daphnide; the eye occupies the center 
of the lower part of the head margin, and is of moderate size; the pig- 
ment fleck is near the base of the antennules and well removed from 
the eye; the antenne are straight and long, with a sensory bristle 
near the base in front and two bristles athird fromthe end; the second 
antenne are furnished with a powerful basal joint, while each of the 
main subdivisions of the rami has its bristle, which are nearly equal; 
two of the terminal sets are toothed for the basal half and pectinate 
distally, but the others are feathered throughout; the four-jointed 
ramus has a spine on the second joint and a longer one at the end, and 
all the joints of both rami are ornamented with triple series of spines; 
the maxille are three spined at the end and are in almost constant 
motion; the first pairs of feet have curious comb-like bunches on some 
of the sete; the abdomen is very short and terminates in inconspicuous 
teeth, the posterior part of the abdomen being ornamented with teeth 
flattened longitudinally so as to look like spines from the side; the 
last foot is simple but bears a large appendage; the posterior third of 
the shell is fringed by extremely minute spines, but anteriorly by 
lanceolate stiff spines flattened longitudinally like the spines of the 
abdomen; the caudal sete are seated on a high prominence of the ab- 
domen, and are fringed along their whole length, not merely at the 
end. The female is 1.0 mm. long, the male 0.5 to 0.6 mm., in which 
sex the antennules have more numerous lateral bristles, the first foot 
has a claw and the back is less elevated. The semen bodies are irreg- 
ularly round with small nuclei. 
GENUS STREBLOCERUS Sars. 
In form like Macrothrix laticornis, head terminating in a long ros- 
trum bearing the long, twisted antennules. Antennules very large, 
curved backward and outward. Head not separated by a distinct 
