ENTOMOSTRACA OF MINNESOTA. 239 



more nearly represent our present knowledge of the genus than that of 

 the previous edition. Unfortunately the key must be based on the 

 statements of other authors, and in this genus it is rare to find com- 

 plete agreement between the published descriptions. The best thing 

 a student can do is to disregard much of the synonomy and make an 

 exhaustive study of a species from a large number of individuals in 

 one locality and then cautiously extend the range of work to include 

 adjacent stations. 



KEY TO THE GENUS ALONA. 



I. Macula cerebri much larger than the eye. . sang'uiiiea, 239; nioniezi, 240 

 |II. Macula cerebri about as large as the eye. tiliadraug'ularis,240; (affiiiis, 240 



obloiiga, 240;) lepida, 242 (See also intermedia, 244) 



III. Macula cerebri smaller than the eye. 



A. Post-abdomen narrowed toward the end, at least not broadly rounded. 

 a. A single series of anal spines. 



'' Striae oblique to the axis of the shell lacustris, 242 



** Striae parallel to the axis of the shell. 



t Abdomen very long, with long anal spines. (One form of) 



temiicaudis, 242 



ft Abdomen not very long guttata, 243 



h. A lateral as well as an anal series of post-abdominal spines, setae 

 or scales. 



* Post-abdomen long and slender. (Usual form of) tenuicaiidis, 242 

 ** Post-abdomen of ordinary form. 



t Anal spines two. Eow of setae in addition. . deiitata, 244 

 ft Anal spines represented by transverse clusters of bristles. 



intermedia, 244 



ttt Anal spines large, nearly equal piilclira, 245 



tttt Lower anal spines larger porrecta, 246 



B. Post-abdomen broadly rounded below. 



a. Anal spines in a single series Stagnalis, 246 



h. A double series of anal spines. 



* Striae of shell close, fine and oblique elegaus, 247 



** Striae of shell distant. 



t Striae oblique ang'lllata, 247 



tfStriae parallel to the longitudinal axisof the shell, coronata, 247 



(Not noticed in the key COStata, 245; barroisi, 248) 



*Alona sanguinea P. E. Mueller. 



Plate LXII, Fig. 20. 



Body nearly rectangular; ventral margin nearly straight, with short 

 sette; posterior angle rounded, unarmed. Beak short; pigment fleck 

 much larger than the eye. Post- abdomen large, the end truncate, 

 broadened; posterior margin rounded, with a series of spines and a 



