7o6 



FRESH-WATER BIOLOGY 



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

 sirople; 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 mucro. 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- and 4-iointed ramus. Post- 

 abdomen somewhat quadrate; anus terminal; spines small and inconspicuous; claws set on a 

 cyUndrical process. $ smaller than J , with short, blunt rostrum; large free antermules; book 

 and long flagellum on first foot. 



Little work has been done in this country on this very difficult 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. MiiUer) 1785. 



Two series of spinules on 

 daws, 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 antermules. Antennules 

 moderate or short (var. 

 brevicornis) ; sometimes re- 

 curved at apex (var. cor- 

 nula). Transparent or 

 clear yellowish. Length, 9 , 

 0.3-0.5 mm.; $, 0.23-0.4 

 mm. 



Very common and very 

 variable. In open water 

 of lakes, in weedy mar- 

 gins, in pools and marshes. 



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

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



79 (78) Claws with basal series of spinules only 8p 



