PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 15 



segments and strongly curved. The first three segments are short, the fourth or fifth 

 is as long as broad, and the fifth or sixth to the ninth or twelfth are longer than broad, 

 less so in old than in young individuals. Those beyond gradually become shorter until 

 the distal are broader than long. On one of the segments between the sixth and the 

 fifteenth a small projection appears at the distal end of the dorsal side; this develops 

 gradually into a strong low keel that occupies nearly the whole of the dorsal side of the 

 more distal segments. The terminal claw is small, and the opposing spine is not well 

 developed; when most strongly developed it is more keellike than spinelike. In the 

 old individual both claw and spine are small. In proportion to the size of the animal the 

 cirri are much shorter than those of N. mrilis, with but half as many segments, which are 

 not uniform in length as in that species. 



No basals are visible. 



The radials and the IBr scries resemble those of N. virilis. The radials are large and 

 hi lateral contact, entirely or except at the distal angles. The proximal margin of the 

 radials is convex: the distal border is broader and concave. The IBr! are free laterally 

 and are narrower distally than proximally. A synarthrial tubercle is formed with a 

 posterior projection from the axillary. The two proximal edges of the IBr 2 (axillary) 

 are nearly straight and the distal edges are concave. 



The 10 arms in the largest specimen are 105 mm. long and are composed of about 1 14 

 brachials. The first brachials are much shorter than, and are slightly incised by, the 

 second. The two brachials beyond the first syzygial pah 1 , the fifth and sixth, are almost 

 rectangular and, more especially in the larger specimens, broader than long. Those 

 beyond as far as the third syzygy are wedge-shaped, almost triangular, and nearly as 

 long as broad. Distally the brachials become less triangular and more quadrate and, 

 toward the end of the arms, as long as or longer than broad. Toward the end the arm 

 becomes zigzag because each brachial bends toward the side from which its pinnule 

 springs. 



Syzygies are numerous. The first is normally between brachials 3+4, but in one 

 arm of one specimen it is between brachials 11 + 12. The second is usually between 

 brachials 9 + 10, though it occurs also between brachials 6 + 7 or 8+9, and between any 

 two from the tenth to the sixteenth. The third is usually between brachials 14+15, 

 and the distal intersyzygial interval is from 2 to 5 muscular articulations. 



The oral pinnules are short and stout, and taper to blunt tips. They arc composed 

 of a small number of rounded segments each of which, except perhaps for the first, is 

 slightly longer than broad. PI is always heavier and slightly longer than P 2 and P 3 , 

 which are of the same length. P! is not entirely free; its first 2 to 4 segments are directly 

 attached to the disk, and 1 or 2 beyond are connected with the disk by a web of tissue. 

 The first segments of the other oral pinnules are similarly attached to the arms by webs 

 of tissue. 



In the younger specimens P, is 5.5 to 7 mm. long and is composed of 8 to 10 seg- 

 ments. P 2 and P 3 are 5 or 6 mm. long with 7 to 10 segments. In the old specimen from 

 station 1948, P, is 11 mm. long, with 13 segments, and P 2 and P 3 are 9 mm. long, 

 with 12 segments. P 4 is usually an oral pinnule and is, variable even on the different 

 arms of a single individual. It is usually longer than P 2 and P 3 , though some times 

 of the same length, with 7 to 12 segments. It is sometimes a genital pinnule of greater 

 length and with more segments. 



The number of genital pinnules on one side of the arm hi the 9 younger specimens 

 varies from 8 to 19, and is 23 hi the older specimen. The gonads lie at their bases as 



