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\ 56 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
VI. Male with the antepenultimate joint of the right antenna not armed 
with hook or plate. 
a. Internal ramus of the right male fifth foot longer than the basal 
joint of the outer ramus. 
* Internal branch of right fifth foot of the male one-jointed. Oregonensis, 72; 
pallidus, 73; piscinze, 74; laciniatus, 74. 
** Internal branch of the right fifth foot of the male two-jointed. . castor, 74; 
glacialis, 75; mirus, 75; sancti-patricii, 75. 
b. Internal ramus of the right fifth foot of the male shorter than the 
basal joint of the outer ramus. 
* This internal ramus greatly expanded. . . . . . .  Jlilljeborgi, 76. 
** Tnner ramus of the right fifth foot of the male not enlarged. 
+ Abdomen asymmetrical. . . roubaui, 76; tyrelli, 76; theeli, 77; 
lobatus, 77; affinis, 77; amblyodon, 78; mississippiensis, 78. 
(D. birgei, 79.) 
Diaptomus asiaticus Uljanin. 
PCAP EH OX MEG i. 
Uljanin ’75; De Guerne and Richard ’89. 
This seems to be a curious depauperate form found by Uljanin in 
the desert of Kisil-Kum, Siberia. The peculiar form of the fifth feet 
of the male together with the hook at the extremity of the right male 
antenna serve to distinguish it. Length of female, 1.76 mm.; of an- 
tenne, 1.31 mm. Color, red. 
Diaptomus denticornis Wierzejski. 
PLATE X, Fia. 4. 
Sars ’63 (castor); Wierzejski ’82 and ’83 (gracilis), and ’87. 
This is one of the large species (3.0 mm. long). It was identified 
by Sars with D. castor. Although originally found in Scandinavia, 
it appears to occur in suitable stations throughout Europe. The an- 
tenn are short, scarcely exceeding the third abdominal segment. 
The last segment of the right antenna of the male hooked, the penul- 
timate segment with a hyaline plate. The figures illustrate the char- 
acters of the fifth feet. 
Diaptomus serricornis Lilljeborg. 
PLATES VIII, Fria. 14; 1X, Fia. 12. 
Lillieborg ’88; De Guerne and Richard ’89. 
A species of moderate size 1.80 mm. long, characterized by the fact 
that the antepenultimate of the right male antenna bears a projecting 
plate furnished distally with coarse teeth. The fifth feet of the male 
are also characteristic. The last thoracic segment bears small spines 
laterally. The caudal stylets about equal in length the two preceding 
segments combined. The antennz in the female nearly reach the end 
of the stylets and are said to be 23-jointed. The species was found 
in lakes of the Russian tundras. 
