THE WATER FLEAS (CLADOCERA) 



731 



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



214 (215, 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, 9 . 0.5-0.6 mm. 



New England, Wisconsin, Michigan, Louisi- 

 ana; not common. 



FIG. 1 1 48. Chydorus faviformis, cast shell. 



0.1 MM. 



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



Chydorus bicornutus Doolittle 1909. 



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. 1149. Chydorns bicornutus. (After Doolittle.) 



O.I MM. 



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 Lilljeborg 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, 9 > -5 mm - 



Lake Superior, Wisconsin, Michigan; rare. 



This species is C. rugulosus Forbes. 



FIG. 1150. Chydorus gibbus. 



O.I MM. 



