THE WATER FLEAS (CLADOCERA) 



699 



44(41) Vertex angulated spinous. Blunt, rounded posterior spine on 

 valves in old individuals. Ocellus rhomlx)idal or tri'inRuiar 

 rarely elongated. . . Simocephulus scrnUaius (KiKh} iSjii' 



Anal spines 8-12, the larser l)cnt and ciliatr. (laws wnf, „„c 

 denticles. Color yellow or brownish. I^cnKth. 9 , 3.8- j o mm 

 $ , to 0.8 mm. 



Common everywhere amonp weeds; the most abundant m>c- 

 cies. Very variable in outline of head. 



Fig. 1075. Simoctphalus icrruUtuu 



0.1 MM. 



45 (40) Valves obscurely reticulated and with some striar. Posterior an<i 



ventral margins straight, the latter extended into a \yo\i\\ or 



spine Scapholcbcris Schocdlcr 1S58 . . 46 



Body not compressed; shape more or less quadrate. Cervical sinus deep. F'omicrs and 

 rostrum well developed. Head small, depressed. Valves almost rectan^'ular. the infcro- 

 posteal angle of each produced into a longer or shorter spine; ventral margin with short, fmc 

 setae. Claws denticulate, not pectinate. One abdominal projection devclopc*!. .\ntcnnulc« 

 small, about alike in both sexes, borne behind the rostrum. .Summer eggs numerous; one 

 ephippial egg. $ much like 9 J hook on first foot. 



46 (47) Color usually dark, often nearly black. 



Scapholeberis mucronata (O. Y. MuUer) 1785. 



Valves arched dorsally in old 

 specimens; fK)sti-rior and ven- 

 tral margins straight; at their 

 junction a spine often sh«jrt, 

 but often very long; in v«r. 

 armata Merrick as long as ven- 

 tral margin of valve, .\nten- 

 nules very small. almo!it im- 

 movable, set iK'hintI l>eak. 

 Post -abdomen short and broad. 

 rounded at i)i)sterior end; $-ii 

 anal teeth. U-ngth. 9 . 0.8-1 .0 

 mm.; $ . ca. 0.5 mm. 



The form with frontal spine 

 has never In-cn foun<l in the 

 United .*>tates. Common ever)'- 

 where in pools and lakes in 

 weedy water, or swimming on 

 Fig. 1076. Scapholeberis mucronata. its back near or at the surface. 



47 (46) Color whitish or greenish; transparent or opaque, not black. 



Scaphohbcris iiuritii (Fischer) 1840. 



Head larger than in mucrouata, rostrum long, lying ag.tinst 

 margin of valves, .\ntennules l)ehind rostrum, conical, large, and 

 movable; sense-hair about middle. Valves with blunt pn.jr. tion 

 at infero-posteal angle, ob.scurely striate and n-ticulate m (rxrtit. 

 and with small elevations elsewhere. U-ngth. 9 . ca 1 o mm ; 



Not^ common; in weedy ix)ols and margins of lakes. Northern 

 states. 



Fig. 1077. ScaphoUbcris aurito. 



0.1 MM. 



