86 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
first printed in the tenth annual of this survey, the edition was not 
distributed till after the August issue of the American Naturalist of 
1882, containing the description above alluded to. Forbes says this 
genus has antennz 23-jointed; all the specimens we have gathered 
from Minnesota to Alabama had 24-jointed antenne. The original 
description of ‘‘Potamoichetor”’ is appended. 
‘‘Cephalothorax six-jointed, distal segments evident; abdomen, in 
the male, five-jointed, in the female four-jointed; antenne 24-jointed, 
the right geniculated as in Centropages (—Ichthyophorbia); first pair 
of feet with the rami both three-jointed, like the following; 
feet of the fifth pair, in the female, like the preceding, but with a 
spine of the joint preceding the terminal one enlarged and divaricated 
somewhat as in Centropages; in the male, the right with a two-jointed 
outer ramus, the terminal joint of which is spined and bears near its 
base a blunt expansion of its inner margin; outer ramus of left foot 
three-jointed, armed with unequal spines; inner branches smaller, 
similar, three-jointed; the terminal joint bearing curved spines; ovary 
and testes as in Diaptomus, with which the mouth parts agree in the 
main; eyes median, confluent.”’ 
Ovisac very large, elongate. 
Our own experience is that the single species of this genus prefers 
estuaries of running water. Forbes, however, has taken it from 
swamps and wayside pools. 
* Osphranticum labronectum Forbes. 
PLATES XII, Fias. 1-8, 13, 14; LIX, Fias. 7, 8. 
Forbes ’82; Herrick ’82 (Potamoichetor fucosus), ’84 and ’87; De Guerne and 
Richard ’89. 
‘‘Rather slender, and in size, as well as general appearance, resem- 
bling the smaller forms of Diaptomus; antenne rather stout, reaching 
but little beyond the feet, appendaged as in Diaptomus, in the male 
strongly geniculated, but somewhat variously so; the six joints pre- 
ceding the terminal four are thickened; those preceding the joint or 
hinge are arcuate on the distal margins; the secondary antenne are 
about asin Diaptomus; mandibular palp two-branched, the outer three- 
jointed, the inner two-jointed; the terminal joint of the shorter branch 
bearing seven sete, of the other four, the proximal joint of the former 
with three stout spines; the maxille nearly like Diaptomus; the pro- 
cesses have respectively the following numbers of sets: the basal 
plate eight, the small processes at base of posterior branchial append- 
age one, the appendage itself twelve, terminal portion three groups, 
first containing nine, the second three, and the third four or five, the 
upper of the anterior processes two, and the lower three; fifth feet 
nearly like the others in size; the right in the male having the outer 
