THE WATER FLEAS (CLADOCERA) 



699 



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

 valves in old individuals. Ocellus rhomboidal or triangular, 

 rarely elongated. . . Simocephalus serrulatus (Koch) 1841. 



Anal spines 8-12, the larger bent and ciliate. Claws with fine 

 denticles. Color yellow or brownish. Length, 9> 2.8-3.0 mm.; 

 $ , to 0.8 mm. 



Common everywhere among weeds; the most abundant spe- 

 cies. Very variable in outline of head. 



FIG. 1075. Simocephalus serrulatus. 



O.I MM. 



45 (40) 



Valves obscurely reticulated and with some striae. Posterior and 

 ventral margins straight, the latter extended into a point or 



spine Scapholeberis Schoedler 1858 . . 46 



Body not compressed; shape more or less quadrate. Cervical sinus deep. Fornices and 

 rostrum well developed. Head small, depressed. Valves almost rectangular, the infero- 

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

 setae. Claws denticulate, not pectinate. One abdominal projection developed. Antennules 

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

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



46 (47) 



O.I MM. 



47 (46) 



O.I MM. 



Color usually dark, often nearly black. 



Scapholeberis mucronata (O. F. Muller) 1785. 



Valves arched dprsally in old 

 specimens; posterior and ven- 

 tral margins straight; at their 

 junction a spine often short, 

 but often very long; in var. 

 armata Herrick as long as ven- 

 tral margin of valve. Anten- 

 nules very small, almost im- 

 movable, set behind beak. 

 Post-abdomen short and broad, 

 rounded at posterior end; 5-6 

 anal teeth. Length, 9 , 0.8- 1 .o 

 mm.; $ , ca. 0.5 mm. 



The form with frontal spine 

 has never been found in the 

 United States. Common every- 

 where in pools and lakes in 

 weedy water, or swimming on 

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



Color whitish or greenish; transparent or opaque, not black. 



Scapholeberis aurita (Fischer) 1849. 



Head larger than in mucronata, rostrum long, lying against 

 margin of valves. Antennules behind rostrum, conical, large, and 

 movable; sense-hair about middle. Valves with blunt projection 

 at infero-posteal angle, obscurely striate and reticulate in front, 

 and with small elevations elsewhere. Length, 9 c 3 - I - mm.; 

 $, 0.5 mm. 



Not common; in weedy pools and margins of lakes. Northern 

 states. 



FIG. 1077. Scapholeberis aurita. 



