somal segment is nearly equal to the length of 

 the first metasomal segment (fig. 5). The endo- 

 pod of the left fifth leg (fig. 6) is not as well 

 developed as that of the fourth leg; in some 

 specimens its setae are almost completely re- 

 duced (fig. 7). 



Neocalanus robt(stior (Giesbrecht, 1888) 

 (Plate 1, figs. 8-10) 

 Occurrence 



Sta. 3. 28 adult females, 4.03 to 4.32 



mm.; 7 adult males, 3.16 to 3.45 



mm. 

 Sta. 5. 7 adult females, 4.03 to 4.22 



mm.; 11 adult males, 3.36 to 3.45 



mm. 

 Sta. 7. 12 adult females, 4.12 to 4.41 



mm. ; 3 adult males, 3.36 to 3.55 



mm. 



Remarks 



This species can easily be distinguished from 

 A^. gracilift — the female by its large size, the 

 shape of the genital segment, and the shape of 

 the external margin of the maxilla, and the 

 male by the location of the small process at the 

 dorsodistal margin of the cephalosome (fig. 8). 

 The left fifth leg of the male (fig. 9) has a rudi- 

 mental 3-segmented endopod, the distal seg- 

 ment of which, in some specimens, has 2 or 3 

 small setae (fig. 10) . 



FAMILY EUC.4LANIDAE 



Eucalanus attenuaUis (Dana, 1849) 

 (Plate 1, figs. 11-17; plate 2, figs. 1-16; plate 

 8, figs. 1-13) 



Occurrence 



Both small and large forms were taken. 



Small form 



Sta. 3. 1 adult female, 4.51 mm. ; 



1 fifth copepodid male, 3.55 mm. 

 Sta. 5. 2 adult females, 4.51 to 4.70 mm. ; 



1 fifth copepodid male, 3.64 mm. 

 Large form 



Sta. 5. 1 fifth copepodid male, 5.56 mm. 

 Sta. 7. 3 adult females, 6.62 to 6.91 mm. ; 



1 fifth copepodid female, 5.66 



mm. ; 



4 fifth copepodid males, 5.56 to 



6.04 mm. 



Sta. 9. 2 fifth copepodid females, 5.47 to 



5.56 mm. ; 



1 fifth copepodid male, 5.47 mm. 

 Sta. 13. 5 adult females, 6.52 to 6.81 mm. ; 



25 fifth copepodid females, 5.56 



to 6.14 mm. ; 



1 adult male, 6.00 mm. ; 



28 fifth copepodid males, 5.56 to 



6.04 mm. 

 Sta. 15. 11 adult females, 6.52 to 7.00 



mm. ; 



14 fifth copepodid females, 5.47 



to 5.95 mm. ; 



17 fifth copepodid males, 5.56 to 



6.04 mm. 



The present collections have two forms of E. 

 attenuatus differing from each other mainly in 

 size of the body and in number of setae of the 

 mandibular palp. The small form seems to 

 agree in anatomical details with the description 

 given by Giesbrecht (1892) to this species, but 

 the large form apparently has not been de- 

 scribed. Both forms are described below. 



Small Form 



The small form is described in less detail 

 than the large form and mainly for comparison. 



Description of Female 



In a specimen 4.70 mm. long the proportions 

 of the prosome to the urosome are about 7.2:1 

 (plate 1, fig. 11). Tho.se of the 2 free urosomal 

 segments and the caudal furca are 49:16:35 

 (plate 1, figs. 13 and 14). The genital segment 

 is wider than long (55:45). The height of the 

 produced, triangular part of the forehead 

 (plate 1, fig. 12) is about four-fifths the length 

 of the base. The mandibular palp (plate 1, fig. 

 15) has 2 setae on the basis, 4 setae on the sec- 

 ond endopodal segment, and 6 setae on the 

 exopod. 



Description of Immature Male 



Only 2 fifth copepodid males were found. 

 These immature forms can readily be identified 

 by the setal arrangement on the mandible, 

 which is the same as that of the adult female. 



Large Form 



Detailed descriptions of adult females, fifth 

 copepodid female, adult male, and fifth copepo- 

 did male follow. 



CALANOID COPEPODS FROM NORTH PACIFIC 



533 



