452 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



PI is 20 mm. long with 50 segments. The first 4 or 5 segments are about twice as 

 broad as long, and the remainder are all broader than long. The third and following 

 segments have a prominent carinate crest on the side toward the arm tips. On the 

 third the crest is broad and gently convex, on the fourth and fifth the process is bluntly 

 pointed, and on the segments following the crest is long and high, rising to a height 

 of half the width of the segment or more, with the outer edge straight and parallel 

 to the longitudinal axis of the segment. These prominent crests on the segments 

 present in general the same effect as the combs on the proximal pinnules of the co- 

 masterids, but the outer edge is straight so that they are in shape oblong with the corners 

 rounded, and they are situated on the side of the segments toward the arm tip instead 

 of on the opposite edges. The pinnule is slender, evenly tapering, flagellate, and 

 flexible. 



P 2 is 12 mm. long with 18 segments, of which the first 3 are twice as broad as long, 

 the seventh is about as long as broad, and those following gradually increase in length, 

 the distal being twice as long as broad. The pinnule is slightly stouter basally than P : , 

 tapers more gradually, and is less flexible. It tapers gradually to a point, and there is 

 no modification of the segments. 



P 3 is 10 mm. long with 20 segments and resembles P 2 . 



P 4 is 12 mm. long with 19 segments. 



P 6 is 12 mm. long with 18 segments, very slightly stouter basally than P 4 . The 

 pinnule increases slowly in width to the fifth and sixth segments, the seventh segment 

 tapers strongly distally, and the remaining segments are slender. Viewed dorsally, 

 the first 2 segments are very short, the fourth is about as long as broad, the seventh is 

 about twice as long as the central width, and those following soon become about 4 

 times as long as broad. The fourth to seventh segments have their ventrolateral 

 edges produced and broadly rounded, these flanges serving as a protection for the 

 gonad. In lateral view the fourth to seventh segments are seen to be broadened, this 

 broadening being greatest on the fifth. The seventh and eighth taper distally, and 

 the ninth and following are slender. 



Pa is 22 mm. long with 36 segments. Viewed laterally, it increases in width to the 

 fifth and sixth segments, tapers on the seventh to ninth, and is slender with increasingly 

 elongate segments from that point onward. The fourth to sixth segments have a slight 

 flangelike production of the ventral edges. 



The following pinnules are similar, about 20 mm. long, with the third to seventh 

 segments somewhat expanded and with their ventrolateral edges produced into a thin 

 narrow flange. The genital pinnules have much the same appearance as those of the 

 species of Perissometra. The ventral surface of the pinnules is completely enclosed 

 by large covering plates imbricating distally, each of which bears a more or less elongate 

 fingerlike process extending over the median line, the processes of the plates on the two 

 sides of the median line exactly dovetailing over the median line. 



In the largest specimens from Aurora station 12 the arms are about 160 mm. long, 

 or somewhat less than twice as long as the longest cirri. 



There is very considerable variation in the height of the middorsal carinate proc- 

 esses on the brachials, particularly on the more or less oblong brachials before the third 

 syzygy. In occasional specimens (for instance from Aurora station 1) the processes 

 on these proximal brachials are almost wholly obsolete, being represented only by low 



