720 



FRESH-WATER BIOLOGY 



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



Euryalona Sars 1901. 

 Sole American species Euryalona occidentalis Sars 1901. 



Euryalona occidentalis Sars. 



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- 

 Z with strong hook; vas deferens opens on 

 Color dark brown-yellow. Length, 9 . to 



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 m weedy pools and lakes. 



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



none 13^ 



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



136 (168) Rostrum not greatly exceeding antennnles i37 



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 distally. 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) 12-15 marginal denticles. 



Oxyurella tenuicaudis (Sars) 1862. 



Marginal denticles very small near anus; 

 the distal 4-5 much larger; the penulti- 

 mate largest. Length, 9, ca. 0.5 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. 1 1 25. Oxyurella tenuicaudis. Apex of 

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



