ENTOMOSTRACA OF MINNESOTA. 55 
The American literature has been unfortunate in respect to this 
genus, chiefly because the European species were so imperfectly de- 
seribed that satisfactory differentiation was impossible. Within the 
last few years this difficulty has been removed, and the work of 
De Guerne and Richard has laid the foundation for careful discrimina- 
tion. It is thought advisable to reproduce the essentials of the de- 
scriptions of the known species so that other students may have the 
means of identifying our species, only a small part of which are as 
yet satisfactorily known. 
KEY TO THE GENUS DIAPTOMUS. 
I. Male with a hooked al on the last joint of the right anten- 
na. . . asiaticus, 56; denticornis, 56. 
II. Male iii a eeettatedl nlite on the antepenult segment of ite right 
antenna. . . serriconis, 56; wierzejskii, 57; pectinicornis, 57; 
trybomi, 57; hircus, 57. 
Ill. Male with the appendage of the antepenult segment of the antenna 
prolonged into a curved hook longer than the penultimate seg- 
MMENibasws oe, ees . . @eiseni, 58; franciscanus, 58. 
IV. Male with the Baran of the pnt peaalticente joint of the an- 
tenna straight, and as long as or longer than the penultimate 
joint. 
a. The basal joint of the right foot of the fifth pair in the male with 
an external accessory process. . . . . . Salinus, 59; laticeps, 59. 
b. The basal joint of the right male fifth foot without a process. . minutus, 59; 
ashlandi, 60; sicilis, 60; baccillifer, 61; Shoshone, 61. 
V. Male with the appendage of the antepenultimate joint of the an- 
tenna shorter than the penultimate joint. 
a. The first segment of the abdomen unsymmetrical, with a strong 
process upon therightside. . signicaudatus, 63; incongruens, 63; 
gibber, 63. 
b. The antepenultimate segment of the antenna of the male witha 
hyaline appendage along its outer margin. 
* Inner ramus of the right fifth foot of the male shorter than the 
basal segment of the externalramus. . Zachariasi, 64; leptopus, 64. 
** Tnner ramus of the right fifth foot of the male longer than the 
basal segment of the outer ramus. . .  tatricus, 65; coeruleus, 65. 
¢. The antepenultimate segment of the right antenna of the male 
without a straight lamina. 
* The process of that segment very shortand obtuse. . . . gracilis, 66. 
*s The process of the antepenultimate segment of the right male 
antenna long and pointed. 
+ Inner ramus of the left fifth foot of the male shorter than or 
nearly equal to the basal joint of the outer ramus. . orientalis, 66; 
stagnalis, 66; albuquerquensis, 67; lintoni, 68. 
+t Inner ramus of the left fifth foot longer than the basal joint of 
the outerramus. . . . . Siciloides, 69; novamexicanus, 70; 
sanguineus, 71; minnetonka, 71; armatus, 72. 
