12 MICHIGAN FISH COMMISSION— BULLETIN NO. 5. 



and 21st have one seta; the 6th has none; the 25th has four setae, one of 

 which is plumose; the 8th and 12th have, in addition to the ordinary and 

 "sensory setse a hook-like spine. 



The left antenna of the male is armed like the female antenna. 



The right antenna of the male is 22- jointed, the 19-21 being united in 

 one, and the 22d and 23d. The joint is between the 18th and 19th. ; The side 

 of the 17th is produced into a blunt spine, and the 18th and 19th are armed 

 on the inner margin with rows of minute spines. The number of the sensory 

 seta3 is the same as in the left antenna and in the antenna of the female, 

 and not greater as stated by Nordqvist. In fact the differences in the 

 armature of the right and left antennae are only apparent, and are occa- 

 sioned by the coalescence of the 19th-21st and the 22d and 23d joints. 



It has seemed be3t to me to figure the swimming feet and describe them 

 in some detail, in order to get a basis of comparison with similar forms. 



In the first foot both the first and second basal joints are armed inter- 

 nally with a plumose seta. The first two joints of the exopodite have no 

 external spines; the terminal joint has two external spines, two apical 

 setae— the outer spinulose on its outer margin — and three internal setae. 

 The terminal joint of the endopodite has one internal seta, two apical, and 

 three internal. 



The second, third and fourth feet have no seta on the second basal joint, 

 and the first and second joints of the exopodite have each an external spine. 

 In all the feet except the first there are groups of two or three minute 

 spines at the bases of the spines of the exopodite. 



The second and third feet are alike. The terminal joint of the exopo- 

 dite has four internal setae, and the terminal joint of the endopodite has 

 two external setae and four internal. 



The fourth foot is like the second and third except that the terminal 

 joint of the endopodite has three internal setae. The fifth feet have no 

 setae on the basal joints. The second joint of the exopodite in the female 

 is prolonged internally into a hook-like expansion. The exopodites of the 

 male are two jointed, the terminal joints having a peculiar construction 

 more easily understood from the figure than from any written description. 

 The terminal joints of the endopodite in both male and female are armed 

 with two external, two apical, and two internal setae. 



FAMILY CYCLOPIDiE.— Genus CYCLOPS Muller. 

 KEY TO SPECIES OF CYCLOPS. 



Antennae 17-jointed, 



Fifth foot one-jointed, armed with one spine and two 



long setae — a large species of dark color, ater. 



Fifth foot two-jointed, 



Second joint of fifth foot armed with seta and short 

 spine, 

 Terminal joint of outer branch of swimming feet 

 armed externally with three spines, 



Furca of moderate length — occurring in pools, Americanus. 



Furca elongated, outer f ureal seta abbreviated to a 



short, thick spine — limnetic in habit, brevispinosus. 



