THE WATER FLEAS (CLADOCERA) 



733 



224 (220, 223) About 0.5 mm. Antennule with one olfactory seta proximal 

 to cluster at end Chydorus ovalis Kurz 1874. 



O.2 MM. 



FIG. 1154. Chydorus ovalis. Entire specimen and 

 antennule. 



Form round or broad oval. Post- 

 abdomen with rounded apex; 12-15 

 marginal denticles. Claws with 2 basal 

 spines, the proximal minute. Color 

 yellow, transparent. Length, 9 to 

 0.6 mm.; cf (European), 0.5 mm. 



Rare; Nebraska. 



225 (217) Ventral edge of keel of labrum with one or more teeth. 



226 



226 (227, 228) With several teeth; short spine at infero-posteal angle of valves. 



Chydorus barroisi (Richard) 1894. 



Form and size much like sphaericus, though 

 ventral margin is less curved. Keel of la- 

 brum acuminate behind ; serrate, with four or 

 more teeth. Post-abdomen with well-devel- 

 oped pre-anal angle; 10-12 marginal denticles, 

 shortest in middle of row. Color brown-yel- 

 low. Length, 9 ca. 0.4 mm. 



Rare; Lake Charles, Louisiana. 



FIG. 1155. Chydorus barroist. 



O.I MM. 



227 (226, 228) With one tooth; infero-posteal spine present. 



Chydorus hybridus Daday 1905. 



Similar to barroisi but with only one tooth on keel of labrum. 

 Rare; Wisconsin, Michigan, Louisiana, Texas. 



FIG. 1156. Chydorus hybridus. 



