216 GEOL, AND NAT. HIST. SURVEY OF MINNESOTA. 



*Lathoimra rectirostris O. F. Miiller. 

 Plate LVII. 

 Koch '35-'41 (Pasithea rectirostris); Zaddach '44 (Daphnia brachyura); Lievin '48 

 (Daphnia brachyura); Fischer '52 (Daphnia mystacina) ; Lilljeborg '53; Leydig 

 '60 (Pasithea rectirostris); Norman and Brady '67; P. E. Mueller '68; Schoedler 

 '58 (spinosa); Birge '78; Gruber and Weistnann '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 Macrothrix, 

 in this respect resembling the Daphnidw; 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 antenuules and well removed from 

 the eye; the antennae are straight and long, with a sensory bristle 

 near the base in front and two bristles athird from the end; the second 

 antennte 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 setse 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 maxillae are three spiued at the end and are in almost constant 

 motion; the first pairs of feet have curious comb-like bunches on some 

 of the set?e; 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 sette 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 antenuules 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 STKEBLOCEEUS Sars. 



In form like Macrothrix laticornis, head terminating in a long ros- 

 trum bearing the long, twisted anteunules. Antenuules very large, 

 curved backward and outward. Head not separated by a distinct 



