THE WATER FLEAS (CLADOCERA) 73 1 



213(212) Post-abdomen short, broad; pre-anal angle marked. . . . 214 



214 (21S, 216) Shell covered with deep polygonal cells. 



Chydorus faviformis Birge 1893. 



Much like sphaericus in form and size. $ 

 unknown. Color yellow to light brownish. 

 Length, $ , 0.5-0.6 mm. 



New England, Wisconsin, Michigan, Louisi- 

 ana; not common. 



Fig. 1 1 48. Chydorus faviformis, cSLstsheU. 



0.1 MM. 



215 (214, 216) Shell with deep polygonal cells and cuticular ridges. 



Chydorus bicornutus Doolittle 1909. 



0.1 MM. 



Like faviformis in having deep polygonal 

 cuticular cells; but distinguished by the de- 

 velopment of an extraordinary and complex 

 system of thin cuticular ridges, which extend 

 far beyond the ordinary cells. A long horn 

 extends laterally from the middle dorsal region 

 of each valve, from which radiate some of the 

 ridges. $ unknown. Color yellow. Length, 

 9 , to 0.7 mm. 



Maine, New Hampshire, and New Jersey. 



Fig. 1 149. Chydorns bicornutus. (After Doolittle.) 



216 (214, 215) Shell of ordinary type 217 



217(225) Ventral edge of keel of labrum smooth 218 



218 (219) Antero-dorsal surface of valves and head flattened. 



Chydorus gibbus LiUjeborg 1880. 



The curve of the dorsal surface somewhat flattened, 

 both in front and behind, making a sort of hump in 

 center of dorsal margin. Valves reticulated. Head 

 small; rostrum projects from valves in characteristic 

 way. Post-abdomen with 8-10 marginal denticles. 

 Color yellowish to brown. Length, J , 0.5 mm. 



Lake Superior, Wisconsin, Michigan; rare. 



This species is C. rugtdosus Forbes. 



Fig. 1 1 50. Chydorus eibbus. 



0.1 MM. 



