-jqk 6 CRUSTACEA. 



posterior much shorter; anterior of antepenult, about as long as two 

 diameters, and posterior equalling one diameter. The second pair of 

 antennae is rather short, with short seta. The abdomen has three 

 segments, of which the first is largest, and is gibbous below (fig. 6 c) ; 

 this gibbosity is probably not a permanent character. 



Calanus arcuicornis. 



Frons obtusus. Cephaloiliorax k-articidatus, capite angustatus, justice 

 subacutus. Antennas anticce cephalothorace vix lonxjiores, leviter 

 arcuatce, apicibus f route vix poster ioribus, articulis 4 ultimk subcequis, 

 setis perbrevibus, apicalibus articulo valde brevioribus, duabus unci- 

 natis, subapicalibus obsoletis, prope basin paucis brevibus uncinatis. 

 Abdomen angustum, lineare. Styli caudales perbreves, setis strictis, 

 rectis, abdominis longitudine. 



Front obtuse. Cephalothorax four-jointed, nearly obtuse behind, head 

 narrower. Anterior antennas hardly longer than cephalothorax, 

 slightly arcuate towards base, and then straight and inclined a 

 little back, tips nearly in line of beak; first and second joints a little 

 oblong and nearly equal, the last four subequal; setae very short, 

 a few uncinate near base, the apical quite short, much shorter than 

 apical joint, two uncinate, the subapical extremely short. Abdo- 

 men slender, four-jointed, second joint longest. Caudal stylets very 

 short, setae not spreading, straight, about as long as abdomen. 



Plate 72, fig. 7 a, animal, enlarged; b } extremity of antenna. 



Collected, April 9, 1840, in the Pacific, latitude 32° 24' south, lon- 

 gitude 178° 15' east. 



Length, one-sixteenth of an inch. The antennae bend outward, 

 with a single curve, and incline a little backward. The abdomen is 

 slender and rather long, being half the length of the cephalothorax; 

 this, in connexion with the non-spreading setae, makes the species 

 resemble a Candace. The subapical setae are nearly obsolete. 



