7o6 



FRESH-WATER BIOLOGY 



76 (23, 83) Six pairs of feet. Antennules of female large, fixed. Intestine 

 simple; no ceca Family Bosminidae Sars . . 77 



Body short and high often oval or round. Valves cover body and abdomen. Antennules 

 of 9 long, immovably fixed to head. No abdominal process or ocellus. Intestine without 

 convolutions or ceca. Animals small, rarely exceeding 0.5 mm. 



77 (82) Antennules of female approximately parallel to each other, curving 

 backward, fixed to head; olfactory setae on side, usually 

 near base Bosmina Baird 1845 . . 78 



Animal usually hyaline: valves thin; infero-posteal angle with spine — the miicro. Antennules 

 of 9 immovably fixed to head; olfactory setae on side, with small triangular plate above them; 

 distal position of antennules looks segmented. Antennae with 3- and4-jointed ramus. Post- 

 abdomen somewhat quadrate; anus terminal: spin.es small and inconspicuous; claws set on a 

 cylindrical process. ^ smaller than 9 > with short, blunt rostrum; large free antennules; hook 

 and long flagellum on first foot. 



Little work has been done in this country on this very diflacult genus; but it is certain there 

 are not so many species nor so great an amount of variation here as in Europe. 



78 (79) 



Claws with two series of spinules. 



Bosmina longirostris (O. F. Miiller) 1785. 



Two series of spinules on 

 ^ — :^--^— ^-.^ claws, the basal increasing 



in length distally, contin- 

 ued by very fine denticles 

 to tip of claw. Frontal 

 sense-hair about midway 

 \ between eye and junction 

 of antennules. Antennules 

 :% moderate or short (var. 

 ; . j| brevicornis) ; sometimes re- 

 % curved at apex (var. cor- 

 I nula). Transparent or 

 ^^^ clear yellowish. Length, 9 - 

 ■^^ 0.3-0.5 mm.; ^, 0.25-0.4 

 mm. 



Very common and very 

 variable. In open water 

 of lakes, in weedy mar- 

 gins, in pools and marshes. 



0.1 MM. 4 



Fig. 1096. Bosmina longirostris, typical specimen; p, post-abdomen more highly magnified. 

 Rostrum; a, var. cornuta: b, var. brevicornis. 



79 (78) Claws with basal series of spinules only 80 



