134 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Pj to be from 8.5 to 14 mm. (averaging 10 mm.) in length with 20 to 31 (averaging 

 26) segments. 



In the Kristineberg specimen P 2 is 15 mm. long, with 36 segments, intermediate 

 in character between PI and P 3 , and without an ambulacral groove like P t . In five 

 specimens from Bergen, Grieg found P 2 to be from 6 to 8.5 mm. (averaging 7 mm.) in 

 length, with 18 to 24 (averaging 21) segments. 



In the Kristineberg example P 3 is 9.5 mm. long with 21 segments, about as stout 

 basally as P 2 but tapering less rapidly and with a gonad on the fourth to ninth segments. 

 Grieg found in his five specimens from Bergen that P 3 was from 5 to 6 mm. (usually 

 about 6 mm.) in length with 14-16 (averaging 15) segments. 



The following pinnules are similar to P 3 ; the gonads, which are larger on P 4 and 

 P 6 , persist to about the thirtieth pinnules, slowly decreasing in size after about the 

 twelfth. 



The distal pinnules are 13 mm. long, with about 30 segments of which all but the 

 basal are twice as long as broad with slightly spinous distal ends, becoming slowly 

 shorter and more delicate in the attenuate terminal portion of the arms. 



Along the ambulacral grooves of the pinnules there are, as described by Grieg, 

 irregular calcareous structures varying from thick rods with irregular ends, one or 

 both of which may be expanded and perforated, to irregular cribriform plates usually 

 broad basally where they adjoin the pinnular and abruptly narrower distally. 



Gislen (1955) describes a medium-sized specimen, arm length about 70 mm., also 

 from Kristineberg, as having the centrodorsal hemispherical, 2 mm. in diameter, and 

 almost totally covered with cirri. The small dorsal pole is convex. The cirri are 

 XL, 10-16, from 4 to 11 mm. long. The longest segment is only a third again as long 

 as broad and the antepenultimate a fifth again as long as broad. The profile is not 

 noticeably thickened in the distal part. The opposing spine is an indistinct knob. 

 The arm profile is almost smooth dorsally with only slight notches at the articulations. 

 P! with 28 segments is 12 mm. long; P 2 with 19 is 6.5 mm. and P 3 with 15 segments 

 and bearing a gonad is 5.5 mm. long. All the pinnule segments are smooth, without 

 thickened distal ends, the longest ones are a fifth again as long as wide. 



According to M. Sars (1835) this species is light brown, the articulations with 

 whitish transverse bands or dots, the upper surface and the arm tips lighter, and the 

 cirri transparent yellowish white. 



Diiben and Koren (1846) give the color as varying from brownish red and deep 

 bright red to yellow. 



Greig (1913) says that the living specimens examined by him were white and red, 

 the red, however, varying between brownish and bright red. The arms are often pro- 

 vided with alternating white and red bands, or they may be almost uniform white or 

 red, with only the distal or the basal parts respectively red or white. The red color 

 disappears very rapidly when the animal is placed in alcohol. 



Abnormal specimens. Mortensen (1920) has reported a number of interesting 

 cases of aberrant arm structure in this species, all from Kristineberg, Sweden. 



With eleven arms: Three individuals had 11 arms; in two of them the division oc- 

 curred immediately after a syzygy. In one the epizygal is divided longitudinally. 

 In the other one of the branches begins with a syzygial pair. In the third speci- 

 men the brachial below the division is split up somewhat irregularly and the branches 

 have the two lowest segments coalesced. 



