182 Mr. J. D. Dana on some genera of Cyclopacea. 



Eyes simple. 



Antenna, two pairs ; the second often pediform or subcheliform. 



Mandibles 4 — 5 -spino- dentate, sometimes having a subnata- 

 tory palpus. 



Maxilla, one pair ; sometimes with a subnatatory palpus. 



Maxillipeds, one pair; sometimes simple maxillae; at others 

 prehensile, but never at all natatory. 



Feet, six pairs ; the first often prehensile and subcheliform, and 

 either straight or geniculated ; next four pairs bifid and natatory ; 

 the sixth or posterior (corresponding to another pair of natatories) 

 rudimentary or obsolete, but in some genera large in the male, 

 with the right one subcheliform. 



Abdomen 2- to 6-jointed ; two caudal appendages furnished with 

 five setae, some of which may be obsolete ; occasionally short ap- 

 pendages to one or both of the first and second joints. 



External ovaries, one or two, proceeding from the second joint 

 of the abdomen, or what corresponds thereto. 



The genera of this tribe here described may be distributed as 

 follows : — 



1 . Palpi of the mandibles and maxilla obsolete or wanting ; eyes 

 with simple spherical lenses. 

 Family 1. CyclopidvE. External ovaries two. Eyes two, on 

 a single spot of pigment. Abdomen abruptly narrower than the 

 cephalothorax. 



Genus 1. Cyclops, Muller. The two anterior antennae sub- 

 cheliform in the male. [Freshwater species.] 



Family 2. Arpactid^e. External ovary single. Eyes two, on 

 a single spot of pigment. A short appendage near middle of an- 

 terior antennae. Abdomen seldom abruptly narrower than the 

 cephalothorax. [Marine species.] 



Genus 1. Arp actus*, Milne Edwards. Anterior antennae 

 short, and both, in the male, subcheliform ; posterior pair termi- 

 nating in a number of moveable setae. Prehensile feet subcheli- 

 form. 



Genus 2. Setella, Dana. Anterior antennae moderately long, 

 slender, and not subcheliform in the male ; posterior pair and pre- 

 hensile feet nearly as in Arpactus ; short appendages to the first 

 two joints of abdomen ; body slender, and two caudal setae much 

 longer than the body. [Two moveable appendages under the 

 beak.] 



* Milne Edwards has instituted the genus Cyclopsina for a group near 

 Arpactus having the posterior maxillipeds not subcheliform. In the species 

 examined by the writer the subcheliform character is constant, but the 

 moveable finger is sometimes reduced to a very short hook. 



