720 



FRESH-WATER BIOLOGY 



134 d33) Valves tumid in anterior part; post-abdomen narrow. 



Euryalona Sars 1901. 

 Sole American species Euryalona occidentalis Sars 1901. 



FIG. 1124. Euryalona occidentalis Sars. 



cercus. Five pairs of feet; hook on first foot of 9 

 upper (ventral) side of post-abdomen about middle. 

 i.o mm.; $ 0.7 mm. 

 Florida, Louisiana, Texas; not uncommon in weedy pools and lakes. 



General form resem- 

 bling Kurzia, but less 

 compressed; no crest. 

 Valves gaping in front, 

 tumid in infero-ante- 

 rior region; marked 

 obscurely with concen- 

 tric lines; dorsal mar- 

 gin arched. Keel of 

 labrum angled behind 

 but not prolonged. 

 Post-abdomen very 

 long, slender, lobed at 

 apex; with about 20 

 marginal and very fine 

 lateral denticles. 

 Claws straight, armed 

 about as in Campto- 

 $ with strong hook; vas deferens opens on 

 Color dark brown-yellow. Length, $? , to 



135 ( I2 3) Body not greatly compressed; claws with i basal spine, or rarely 



none 136 



For all species with two spines on terminal claw, see 171 ff. 



136 (168) Rostrum not greatly exceeding antennules 137 



137 (167) Rostrum pointed 138 



138 (150) Infero-posteal angle rounded, without teeth 139 



139(144,147) Post-abdomen with marginal and lateral denticles. . . . 140 



140 (143) Post-abdomen relatively long and narrow; marginal denticles 

 numerous, longer dis tally. Basal spine stout and long. 



Oxyurella Dybowski and Grochowski 1894 . . 141 



In general like Alona. Post-abdomen long, slender; with marginal and lateral denticles, 

 the former numerous and ending in a group of large denticles at angle of post-abdomen. Termi- 

 nal claw straight, with one large basal spine, attached some way distal to base of claw. Color 

 yellow or yellow-brown. This genus is the same as Odontalona Birge. 



141(142) 1 2- 1 5 marginal denticles. 



. Oxyurella tenuicaudis (Sars) 1862. 



Marginal denticles very small near anus; 

 the distal 4-5 much larger; the penulti- 

 mate largest. Length, $*> ca - -S mm.; 

 $ , 0.4 mm. 



Widely distributed but not abundant 

 anywhere. New England and Wisconsin 

 to Gulf of Mexico. This species is Alona 

 tenuicaudis Sars. 



FIG. 1125. Oxyurella tenuicaudis. Apex of 

 post-abdomen. (See also Fig. 1129, 6.) 



