THE WATER FLEAS (CLADOCERA) 



727 



190 (187) Rostrum not bent forward IQI 



191 (192) Numerous teeth along whole posterior margin. 



Pleuroxus truncatus (O. F. Miiller) 1785. 



Posterior margin with numerous (more than 20) dose- 

 set teeth; valves striated, the striae on middle of valves 

 nearly longitudinal, the others oblique. Post-abdo- 

 men much hke P. trigonellus, slightly tapering toward 

 apex, angle rounded; 12-14 marginal denticles, increas- 

 ing in size distally. Color yellow-brown. Length, J , 

 ca. 0.6 mm.; d (European), 0.45 mm. 



Nebraska (Fordyce). 



•s. 



Fig. 1138. Pleuroxus truncatus. (European specimen.) 



192 (191) Teeth at infero-posteal angle only . . 193 



193 (196) Post-abdomen long, slender, convex on ventral (upper) side. . 194 



194 (195) Supero-posteal angle sharp but not projecting; infero-posteal 

 angle a sharp point. . . . Pleuroxus hastatus Sars 1862. 



Infero-posteal angle a sharp point, with a very small 

 tooth; valves reticulated, longitudinal marks often more 

 distinct, giving appearance of striation. 16-18 marginal 

 denticles. Color yellow, transparent or opaque; not 

 black unless ephippial. Length, 9, ca. 0.6 mm.; j , ca. 

 0.4s mm. 



Rather rare; New England, Wisconsin, Nebraska, 

 California. 



Fro. 1139. Pleuroxus hastatus. 



0.1 MM, 



19s (194) Supero-posteal angle overhanging; infero-posteal angle rounded, 

 with small tooth in front of it. 



at MM. 



Pleuroxus striatus Schoedler 1863. 



General shape much like P. hastatus 

 but never so high arched as this may be. 

 Valves obviously striated. Post-abdomen 

 long, slender, with 20, or more, marginal 

 denticles. Color dark, especially opaque 

 on dorsal side, often nearly black. Length, 

 9,ca. o.Smm.; cT, ca. 0.6 min. 



In all parts of United States; common 

 among weeds. 



This species is P. gracilis Hudendorf; 

 P. unidens Birge. 



Fig. 1140. Pleuroxus striatus. 



