7i6 



FRESH-WATER BIOLOGY 



ii6 (loo, 107) Antennary setae ; all similar and plumose. 



^ 1-1-3 



Lathonura Lilljeborg 1853. 



Sole species Lathonura rectirostris (0. F. Mliller) 1785. 



General form long-oval, not com- 

 pressed. Valves unmarked; the 

 ventral margin with short, close-set, 

 smooth, lancet-shaped, or spatulate 

 spines. Antennules straight, with 

 sense-hair near base; 2 pairs of sense 

 setae in distal half. Post-abdomen 

 very small, extended behind into a 

 long conical process, which bears the 

 very long abdominal setae; covered 

 with fine spines and setae. Claws 

 small, smooth, or denticulate. Sum- 

 mer eggs, 2 to 10; I ephippial egg. 

 $ like young 9 . with larger anten- 

 nules; 2 lateral sense-hairs, the addi- 

 tional one — the distal — the larger; 

 olfactory setae longer. First foot 

 with hook. Vas deferens opens at 

 claws. Color transparent to clear 

 yellow or greenish. Length, 9 > to 

 i.o mm.; $ , ca. 0.5 mm. 



Widely distributed in weedy mar- 

 gins of lakes but nowhere common. 



Fig. 1 1 17. Lathonura rectirostris. 



117 (22) Fornices extended so as to cover antennules in whole or in part, and 

 uniting with the rostrum into a beak, projecting ventrally in 

 front of antennules. . Family Chydoridae Stebbing . . 118 



0-1-3 



Antennae small, rami 3- jointed; setae =^ or ^ . Labrum with large keel. Five or six 



0-0-3 0-0-3 J . . , 



pairs of feet. No true abdominal process or ephippium. Post-abdomen compressed, jointed to 

 body. Intestine convoluted. Ocellus always present. $ with hook on first foot; large anten- 

 nule; short rostrum. 



118 (119) Anus terminal. 2 hepatic ceca. Summer and ephippial eggs 

 numerous Subfamily Eurycercinae Kurz. 



Sole genus Eurycercus Baird 1843. 



