PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 451 



serrate. After the proximal third of the arm the distal height of the keel diminishes 

 and after the middle of the arm the profile becomes practicalh' smooth, though the 

 keel, which always has a sharply rounded crest, persists to the arm tips. The brachials 

 in the proximal third of the arm have a finely spinous distal overlap, the spines being 

 longest and most prominent at the end of the carination ; in the outer half of the arm 

 the distal border of the brachials is smooth and without an overlap. There is con- 

 siderable variation in the carination on the earlier brachials; it may be high, slender 

 and spinelike, or with a long knifelike edge parallel to the longitudinal axis, some- 

 times having a central notch so that it is more or less divided into two. 



Sj'zygies occur between brachials 34-4, 9-f-lO, 144-15, and distally at intervals 

 of 3 muscular articulations. 



Pi is from 18.5 to 19 mm. in length, flagellate and resembling P, in Ileliometra 

 glacialis, composed of 44 to 50 segments, all of which are broader than long; those in 

 the outer two-thirds are provided with a strong rounded sharply carinate dorsal process; 

 those in the proximal third are provided with a similar process wliich has a straight 

 distal edge parallel to the longitudinal axis of the pinnule. Pj is about half as long as 

 Pi, from 8 to 9 mm. long, with 17 to 19 segments, which are at first much broader than 

 long, becoming on the eleventh about twice as long as broad; the second to fourth 

 bear a strong dorsal carination. P3 is similar to P2 but larger, 10 mm. long with 17 

 segments, of which the outer are slightly more elongated than the corresponding seg- 

 ments of P2. P4 is similar to P3, 10 mm. long. The distal pinnules are 14 mm. long. 



The ambulacral grooves of the genital and distal pinnules, but not those of the 

 arms, are bordered with a row of large and heavily calcified covering plates; these 

 have a broad subquadrangular proximal portion and a narrower rounded cuneiform 

 distal portion which folds down over the ambulacral grooves. Though the plates 

 are large and soUd there is no indication of a division into side and covering plates. 



Color in life. — Arms flesh color, the pinnules pink (note with specknens collected 

 by the Aurora). 



Notes. — In large specimens from Aurora station 12 the longest cirri are 90 mm. 

 long with 81 segments. The first segment is about 4 times as broad as long, the next 

 three are about 3 times as broad as long, the fifth is slightly over twice as broad as long, 

 the sixth is nearly as long as broad, the seventh is one-third again as long as broad, and 

 the ninth to twelfth are nearly t\vice as long as broad. The segments following very 

 slowly decrease in length so that the last eight are scarcely longer than broad. .Vfter 

 about the twelfth the median portion of the distal dorsal border becomes very slightly 

 prominent. In dorsal view the middle third of the distal edge is seen to be slightly 

 bowed outward and serrate. Later this becomes slightly elevated and more strongly 

 serrate, appearing in lateral view as a slight terminal spine directed obliquely forward. 

 Distally this projection slowly narrows, on about the tenth segment from the end the 

 dorsal surface of the segments becoming broadly and roundedh' subcarinate; the median 

 elevation gradually becoming still narrower and more easily evident, the last two seg- 

 ments before the penultimate are distinctly carinate dorsally. The opposing spine is a 

 longitudinally elongate tubercle occupying the distal half of the penultimate segment. 

 The terminal claw is somewhat longer than the penultuuate segment, and is moderately 

 stout and evenly curved. In the outer half the cirri taper very slowly and graduall.v 

 to a slender tip. 



