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 antennae 23 jointed; all the specimens we have gathered 

 from Minnesota to Alabama had 24-joiuted antennte. The original 

 description of '^Fotamoichetor''^ is appended. 



"Cephalothorax six jointed, distal segments evident; abdomen, in 

 the male, five-jointed, in the female four-jointed; antennae 24 jointed, 

 the right geniculated as in (Jentropages (=Ichthi/02)horbia'); 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 Diaptonius, with which the mouth parts agree in the 

 main; eyes median, confiuent." 



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. 



* Ospliranticiim labronectuiii Forbes. 



Plates XII, Figs. 1-8, 13, 14; LIX, Figs. 7, 8. 



Forbes '82; Herrick '82 (Potamoichelor fucosus), '84 and '87; De Guerne and 



Richard '89. 



"Eather slender, and in size, as well as general appearance, resem- 

 bling the smaller forms of Diaptomus; antennre 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 antennae are 

 about as in Diaptomus; mandibular palp two branched, the outer three- 

 jointed, the inner two jointed; the terminal joint of the shorter branch 

 bearing seven setie, of the other four, the proximal joint of the former 

 with three stout spines; the maxillte nearly like Diaptomvs; the pro- 

 cesses have respectively the following numbers of setter 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 



