PART 5 A MONOGRAPH OF THE EXISTING CRIXOIDS 5 



angular space without sockets, unlike N. mortenseni (see fig. 16); the cirri are 

 less than L in number but when the arm length is about 120 mm. the cirri are as long 

 as 45 mm., with about 70 segments; when the arms are 200 mm. long the cirri are 

 about 90 mm., with about 90 segments. 



Description. The centrodorsal is rather large, conical, half again as broad at the 

 base as high, with a roughened dorsal pole. In large individuals the rim of the centro- 

 dorsal is rather deeply concave beneath the radials, so that the interradial angles are 

 quite prominent. The cirrus sockets are arranged in 10 columns of 3 or 4 each, the 2 

 columns in each radial area being externally in contact with those in the neighboring 

 radial areas, but separated from each other by a triangular midradial space. 



The cirri are XXX-XL, stout and rather long, the longest reaching about 45 mm. 

 hi length. Their segments are short, the longest proximal being about a third longer 

 than broad and those in the distal half being all broader than long. The short segments 

 in the outer half of the cirri are produced dorsally into blunt keels or crests which in 

 lateral view are smoothly rounded. The opposing spine is median, short, blunt, and 

 nearly erect. The terminal claw is slightly longer than the penultimate segment, 

 rather slender, and strongly curved. The cirri about the rim of the centrodorsal are 

 mostly turned upward between the arms, and lean over the disk; those nearer the 

 dorsal pole are generally directed downward. 



Above each of the interradial prominences of the centrodorsal, in the angles 

 between them and the radials, there is a small triangular plate interpreted by Mortensen 

 as a basal, though probably the end of a basal ray. 



The radials are short, more than 4 times as broad as long in lateral view, and 

 strongly convex dorsally. 



The IBri are very short, with the distal border excavated by a broad rounded 

 proximal process from the IBr 2 ; then- lateral edges are widely separated from those of 

 then* neighbors, and are strongly convex; then* distal borders are shorter than the 

 proximal. The IBr 2 (axillaries) are slightly broader than long, with the distal borders 

 strongly concave and the lateral angles projecting for some distance beyond the latero- 

 distal angles of the IBr,, and at the same time widely separated from those of their 

 neighbors. 



The 10 arms are 75+ mm,, probably about 125 mm. in length, according to Gislen. 

 All the brachials are short, broader than long, especially in the distal portion of the 

 arms. They are all perfectly smooth and regularly convex dorsally. 



Syzygies are very irregular in their occurrence. In one arm Mortensen gives the 

 syzygies as occurring between brachials 3+4, 8 + 9, 19 + 20 and 28 + 29, while on the 

 other arm of the same pair they were found between brachials 3+4, 9 + 10, 16 + 17 

 and 27+28. Other arms are given as having syzygies between brachials 4 + 5, 10 + 11 

 and 23+24; and between brachials 4 + 5, 10 + 11, 15 + 16, 36+37, etc. Mortensen 

 says that the second syzygy may be found as far out as between brachials 13 + 14 

 or 14 + 15. 



The oral pinnules are stout and short. PI is about 8 mm. long, with 15 segments, 

 which become about as long as broad on the third and about twice as long as broad 

 terminally. P 2 and P 3 are about 9 mm. long in fully grown examples. They resemble 

 P!, but the terminal segments are slightly spinous. P 4 may be also an oral pinnule 

 without an ambulacral groove. The distal pinnules are about 10 mm. long with short 



