134 TWELFTH ANNUAL REPORT. 



iv.-rGrENUS OsPBRAJs'TicuM, Forbes. 



(^Potamoichetor, Herrick.) 



First reported as Potamoichetor before the Minnesota Academy 

 of Sciences in 1879, but owing to a disastrous fire, publication was 

 prevented. Priority probably belongs to Forbes' name, since, 

 although 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 antennas 23-jointed; all the specimens we 

 have gathered from Minnesota to Alabama had 24-jointed anten- 

 nae. The original description of ''Potamoichetor" is appended. 



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

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

 twenty-four-jointed, the right geniculated as in Ceiitropages 

 (=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, thejnght 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 Diap- 

 tomus, with which the mouth parts agree in the main; eyes me- 

 dian, confluent." 



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. 



Sp. 1. Osplirauticuni labronectuni, Forbes. 



(Plate Q2. Figs. 1—8 and 13—14.) 

 Potamoichetor fxicosiis, herrick, Cyclopida? of Minnesota, etc, p. 224. 



"Rather slender, and in size, as well, as general appearance, re- 

 sembling the smaller forms ofDiaptomus; antenna rather stout, 

 reaching but little beyond the feet, appendaged as in Diaptomusi 

 in the male strongly geniculated, but somewhat variously so; the 

 six joints preceding the terminal four are thickened; those preced- 

 ing 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 



