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54 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
tion of the inner branches of the fifth feet in both sexes is especially 
remarkable in view of the three-jointed inner rami of all the other 
feet. The fifth foot in the male is exceedingly like that of Drepanopus 
pectinatus Brady, while those of the female are on the same numerical 
plan; in that genus, however, the male antenna is not geniculate and 
the first foot has the inner ramus one jointed, The genus Hucheta isa 
Somewhat miscellaneous assemblage, with some species resembling 
Pseudo diaptomus. In some respects Centropages is likewise similar. 
GENUS DIAPTOMUS Westwood. 1836. 
Cyclopsina—M ilne-Ed wards. 
Glaucea— Koch. 
Pontie—Ouchakoff. 
Cephalothorax composed of seven segments, of which the cephalic 
two are more or less closely fused to form the head. Abdomen nar- 
row and shorter than the thorax, with three obvious segments in the 
female and four in the male, the last bearing two short stylets. Each 
caudal stylet is armed with five subequal plumose sete and one 
smaller internal bristle. Antenne of the first pair long, 25-jointed; 
in the male geniculate between the eighteenth and nineteenth joint 
and variously thickened and armed, the penultimate segment often 
provided with a curved hook. Second antenne (antennules) two- 
branched; the exterior branch seven-jointed and bearing apically sev- 
eral long sete, inner ramus shorter and two-jointed. The mandibles 
armed with about nine acute teeth and provided with a bi-ramose 
palp. The maxille of the first pair are very short and armed with 
closely set sete. The second maxille, or maxillipeds, are long and 
directed cephalad, seven-jointed. The first pair of swimming feet has 
a two-jointed inner ramus while each of the three pairs following has. 
both rami three-jointed. The fifth pair of feet are dissimilar between 
the sexes and furnish the most important specific characters. In the 
female the two feet are alike and the inner ramus is reduced or rudi- 
mentary, often one jointed. The external ramus develops a strong 
claw from the penultimate joint, while the small apical segment bears 
one or more small spines. The fifth feet of the male are dissimilar, 
five jointed, the inner rami rudimentary, the right limb having a long 
apical claw on the outer branch. 
The species are generally slender and graceful, the antenne often 
exceeding the body in length. Some forms are brilliantly colored 
while most are pellucid. Perhaps most of the species are found in 
open lakes, but a number are restricted to swampy localities and 
others are limited to early spring or late fall and stand in such close 
relations to other species as to strongly suggest a sort of heterogenesis 
like that we have demonstrated in Cyclops. 
