PART 5 A MONOGRAPH OF THE EXISTING CRIXOIDS 497 



Description. The centrodorsal is long columnar, about 5 mm. in diameter through- 

 out and about 8 mm. long, to long truncated conical, about twice as long as broad at 

 the base, with 5 high and sharply rounded interradial ridges, which decrease slightly 

 to considerably in height distally; in each radial area there are 2 regular columns of 

 cirrus sockets, usually 6 in each, which are separated in the median line by a more or 

 less developed low ridge. Only about half the cirrus sockets in each column appear 

 to be functional, the 2 or 3 apical-most in each column having the central canal closed, 

 though being otherwise perfectly formed. The dorsal pole of the centrodorsal is 

 irregular, plane, or slightly concave. 



The cirri are XX-XL, 50, from 55 to 60 mm. in length, strongly compressed 

 laterally. The first segment is short, the second is about half as long as broad, the 

 third is about as long as broad, the fourth is about half again as long as broad, and the 

 following increase in length, the tenth being about 4 times as long as broad. After the 

 fourteenth the length gradually decreases so that the twenty-first is only about twice 

 as long as broad, the twenty-seventh is about as long as broad, and those following be- 

 come very short. Half of the entire length of the cirri is included within the first 16 

 segments. The earlier segments as far as the fourteenth have expanded and produced 

 distal ends which overlap the proximal ends of the segments succeeding. From about 

 the fifteenth segment onward this overlapping gradually dies away ventrally, but dor- 

 sally becomes more pronounced and transforms into a forward projecting spine which 

 occupies progressively more and more of the dorsal surface of each segment, on the short 

 terminal segments becoming a high curved carinate process. The opposing spine is 

 triangular, its base occupying the entire dorsal surface of the small penultimate segment. 

 The terminal claw is conical, not longer than the penultimate segment. 



The ends of the basal rays are visible as a continuation of the high interradial 

 ridges of the centrodorsal to the angles of the calyx, forming high bridges between the 

 deep subradial clefts. 



The radials are very short, U-shaped, with a median and 2 lateral tufts of fine 

 spines or a broad fringe of long glassy spines. The IB^ are very short and band-like, 

 broadly V-shaped, deeply incised by a posterior process from the axillaries, with a 

 broad fringe of fine spines along the proximal border. The IBr 2 (axillaries) are large, 

 rhombic, with all the sides concave, broader than long; the borders all around are 

 fringed with spines, which are much longer on the proximal than on the distal sides, 

 and there is usually also a small tuft of spines in the distal angle. 



The elements of the IBr series and the first 4 or 5 brachials are in close apposition 

 with then* neighbors and sharply and broadly flattened against them. 



The 10 arms are about 130 mm. long. The first brachials are very short with the 

 outer side somewhat longer than the inner and the latter in contact above the anterior 

 angle of the axillary. The second brachials are large and irregular in shape. The first 

 syzygial pair (composed of brachials 3 + 4) is oblong, not quite so long as broad. The 

 following brachials to the tenth are wedge-shaped with more or less developed articular 

 tubercles, and those succeeding are triangular and about as long as broad. After about 

 the thirtieth the brachials become laterally compressed and develop prominently over- 

 lapping distal edges which bear dorsally a fringe of small spines. The distal brachials 

 gradually become more wedge-shaped and finally elongate. The first 6 brachials may 

 have a fringe of small spines on either side. 



