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.; 

 J , to 0.8 mm. 



Common everywhere among weeds; the most abundant spe- 

 cies. Very variable in outline o£ head. 



Fig. 1075. Sijnocephalus serrulatus. 



0.1 MM. 



45 (40) Valves obscurely reticulated and with some striae. Posterior and 



ventral margins straight, the latter extended into a point or 

 spine. . . , Scapholeheris 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) Color usually dark, often nearly black. 



Scapholeheris mucronata (O. F. MiiUer) 1785. 



Valves arched dorsally in old 



specimens; posterior and ven- 

 tral margins straight; at their 

 junction a spine often short, 

 but often very long; in var. 

 armala 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 .0 

 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 

 its back near or at the surface. 



0.1 MM. 



1076. Scapholeheris mucronata. 



47 (46) Color whitish or greenish; 



transparent or opaque, not black. 



Scapholeheris aurita (Fischer) li 



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> ca. i.o mm.; 

 $ , o.s mm. 



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

 states. 



Fig. 1077. Scapholeheris aurita. 



0.1 MM; 



