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... Sanguinea, 239; moniezi, 240 
fil. Macula cerebri about as large as the eye. quadrangularis, 240; (affinis, 240 
oblonga, 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. 
* Striee oblique to the axisoftheshell.. . . . lacustris, 242 
** Strize parallel to the axis of the shell. 
+ Abdomen very long, with long anal spines. (One form of ) 
tenuicaudis, 242 
tt Abdomen not very long. . . ; . « guttata, 243 
b. A lateral as well as an anal series of sett Pdcmnial spines, setze 
or scales. 
* Post-abdomen long and slender. (Usual form of ) tenuicaudis, 242 
** Post-abdomen of ordinary form. 
+ Anal spines two. Row of sete in addition. . dentata, 244 
tt Anal spines represented by transverse clusters of bristles. 
intermedia, 244 
ttt Anal spines large, nearly equal... . . . . pulehra, 245 
tttt Lower anal spines larger. . . . . . . . porrecta, 246 
B. Post-abdomen broadly rounded below. 
a. Anal spinesinasingle series. . . . . . . . Stagnalis, 246 
b. A double series of anal spines. 
* Striee of shell close, fine and oblique. . . . . elegans, 247 
** Strie of shell distant. 
{ Strie oblique. . . . . . angulata, 247 
{tStrize parallel to the lonpitudinalla: axis of the shell. coronata, 247 
(Not noticed inthe key. . . . . . . . costata, 245; barroisi, 248) 
* Alona sanguinea P. E. Mueller. 
PLATE LXIJI, Fia. 20: 
Body nearly rectangular; ventral margin nearly straight, with short 
setve; 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 
