105 4 CRUSTACEA. 



long as the two preceding, while in the O. magellanicus, it is scarcely 

 longer than the next one preceding. 



The three posterior joints of the cephalothorax are nearly half the 

 whole length. Beak directed a little inward. Abdomen four-jointed. 

 There are four pairs of natatories with the fifth rudimentary. Setse 

 of the mouth organs of moderate length. 



Calanus crassus. 



Frons rotundatus. Cephalotliorax crassus, i-articulatus, posticd vix sub- 

 acutus. Antennae anticce corpore breviores, apicibus fronte valde pos- 

 terioribus, setis hrevibus, apicalibus paulo longioribus, subapicalibus 

 minutis, aut obsdetis. Stijli caudales perbreves, setis subcequis, abdo- 

 vnine paulo brevioribus. 



Front rounded. Cephalothorax stout, four-jointed, hardly subacute 

 behind. Anterior antennae shorter than the body, much reflexed, 

 the apices therefore much behind the line of beak, last joint nearly 

 half shorter than penult ; setae short, some near base a little longer, 

 and curving, the posterior of apical joint as long as two terminal 

 joints, the anterior half shorter, those of the subapical joints very 

 short or obsolete. Caudal stylets very short ; setae subequal, not 

 as long as abdomen, slightly spreading. 



Plate 72, fig. 5, animal, enlarged. 



Collected in the Atlantic, May 9, 1842, latitude 9° south, longitude 

 17° 30' west. 



Length, one-sixteenth of an inch. Slightly reddish, with deeper red 

 about the mouth and stomach. The antennse have an oblong basal 

 joint, and some of the setae on the second or third joints are about as 

 long as this joint. These organs curve near base and then extend 

 obliquely backward, hardly curving again. The penult joint has a 

 seta at anterior apex shorter than that on anterior apex of last joint, 

 but none was observed at posterior apex ; and the antepenult joint has 

 neither anterior nor posterior setae, or they are very short. 



