THE WATER FLEAS (CLADOCERA) 



721 



142 (141) About 16 marginal denticles. . Oxyurella longicaudis (Birge) 1910. 



Between Alona and Euryalona in form. 

 Valves with concentric marking. About 16 

 marginal denticles, larger distally; the pe- 

 nultimate much larger, and the ultimate 

 larger still and serrate on concave side. 

 Basal spine stout, attached about one-third 

 way from base of claw. $ unknown. 

 Length, 9 0.5-0.6 mm. 



Rather rare among weeds, Lake Charles, 

 La. 



FIG. 1126. Oxyurella longkcmdis. 



143 (140) Post-abdomen not noticeably narrow; distal denticles not conspicu- 



ously larger. Basal spine small. Alona (most species) . . 151 

 Take up the key at the number indicated where the genus is discussed as a unit. 



144 (139, 147) Post-abdomen with marginal denticles only 145 



145 (146) Post-abdomen large, denticles very small. Alonella diaphana . . 236 

 Turn to the key at the number indicated where the species named is discussed. 



146 (145) Post-abdomen of moderate size; denticles of usual size. 



Alona guttata . . 156 

 Turn to the key at the number indicated where the species named is discussed. 



147 (139, 144) Post-abdomen with numerous clusters of large spines. 



Leydigia Kurz 1874 . . 148 



General shape oval, much compressed but not crested. Head small, extended; keel of 

 labrum rhomboidal with angles blunt or rounded. Post-abdomen very large, compressed, 

 semi-elliptical in form; post-anal part much expanded, with numerous clusters of spines; 

 spines in distal clusters very long. Claws long and slender. Eye smaller than ocellus. $ 

 with blunt rostrum; process on upper (ventral) side of post-abdomen on which vas deferens 

 opens; post-abdomen with spines. Color yellow. 



148 (149) Valves without markings. Leydigia quadrangular is (Leydig) 1860. 

 Keel of labrum with minute setae. Claws with basal spine. Length, 9 to 0.9 mm.; cf , ca. 



0.7 mm. 



In all regions of the country; not common; found singly among weeds. 



149 (148) Valves striated longitudinally. 



Leydigia acanthocercoides (Fischer) 1854. 



Keel of labrum with long cilia. Claws without basal spine. Length, 9 , to i.o mm. or more; 

 cf (European), 0.7 mm. 

 Rare; Louisiana. 



m 



0.2 MM. 



FIG. 1127. Leydigia acanthocercoides. 



