Mr. J. D. Dana on some genera of Cyclopacea. 183 



The name Setella alludes to the seta-like form of the animal, 

 and is from seta, a bristle. 



2. Palpi of the mandibles and of the maxillce prominent and 

 subnatatory. 



Family 3. Calanid^e. External ovary single. Eyes two, the 

 spherical lenses on the same or separate spots of pigment. An- 

 terior antennae very long and slender, without an appendage. 

 Abdomen abruptly narrower than the cephalothorax. [Marine 

 species.] 



a. Posterior thoracic legs rudimentary or obsolete, without ap- 

 pendages. Anterior antenna alike in the two sexes, and never with 

 a geniculating joint. 



Genus 1. Calanus, Leach. Cephalothorax 4-jointed. An- 

 terior antennae multiarticulate, with the front margin neatly se- 

 tiferous, and also the posterior apices of the three terminal joints ; 

 first pair of feet much larger than the maxillipeds, having out- 

 ward lateral motion, but scarcely prehensile ; maxillipeds very 

 short and straight, setigerous ; abdomen short, 2- to 4-jointed. 

 Beak furcate. 



Genus 2. Scribella, Dana. Cephalothorax 4-jointed. An- 

 terior antennse long, 7-jointed ; setae long and pointing in differ- 

 ent directions. Maxillipeds much larger than the first pair of 

 legs, flexed forward, the three terminal joints as long as the basal 

 and setigerous, the setae setulose. Abdomen very long (as long 

 as the cephalothorax) ; two setae to the short basal joint (a plume 

 or capillary appendage to the base of the eight natatory legs ex- 

 tending outward at right angles with the body). 



Genus 3. Acartia, Dana. Anterior antennae few-jointed ; 

 setae long and pointed in different directions ; maxillipeds much 

 larger than the first pair of legs, not flexed, having the terminal 

 joints very short and setigerous, nearly as in the genus Pontella ; 

 the first pair of legs small and short, not prehensile ; the posterior 

 thoracic legs, a single small joint bearing two divergent setae, one 

 quite long and usually standing out from the body. 



The name Acartia is from aicapTos, unshorn, alluding to the 

 long divaricate hairs of the antennae. 



b. Posterior thoracic legs very long and nearly equal; antenna 

 of the two sexes alike, without a geniculating joint. 



Genus 4. Euchirus, Dana. Anterior antennae many-jointed, 

 with several long setae at intervals ; first pair of feet much larger 

 than the maxillipeds, very long and doubly geniculate, the apex 

 flexed downward and furnished below with a pencil of naked setae ; 

 motion of these organs forward in the line of the body, and not 



