A MONOGRAPH OF THE EXISTING CRINOIDS 233 



Description. — The centrodorsal is a thick disk with a rough dorsal surface. 



The cirri are XV-XX, 13-15. The fifth segment is the longest, and those following 

 gradually acquire a dorsal keel which passes into the small opposing spine of the penulti- 

 mate. 



The radials are concealed. The IB^ are short and broad, laterally united, and the 

 IBr 2 (axillaries) are pentagonal, short and broad, with a very obtuse distal angle. The 

 elements of the IBr series and first four brachials are straight edged and sharply flat- 

 tened laterally, and are more or less carinate in the median line. There are small blunt 

 tubercles on the dorsal surface of the IBr series and arm bases. 



The 10 arms are 125 mm. long and consist of nearly 150 brachials. The first 

 brachials are oblong and closely united interiorly, the second more wedge-shaped; from 

 the third to the tenth the brachials are discoidal with the distal edge more or less raised 

 and crenulate, this feature disappearing on the brachials following, which are more 

 triangular and elongate considerably toward the arm tips. The lowest brachials, 

 especially on the younger arms, have a marked median keel which gradually dies away 

 in the middle third, the terminal brachials being quite smooth. Carpenter's figure shows 

 the elements of the IBr series and lower brachials with thickened and produced distal 

 ends, a conspicuous and narrowly rounded median keel fused with the produced distal 

 edge, somewhat everted lateral borders, and several small beadlike tubercles on the 

 dorsal surface. In the larger specimen, which I examined at London in 1910, I found 

 the ornamentation prominent and pearly; the median keels are not quite so prominent 

 as they are shown in the figure. In the smaller specimen the keels are proportionately 

 larger and more regular. 



Syzygies occur between brachials 3+4, again from between brachials 11+12 to 

 between brachials 27+28, and distally at intervals of from 5 to 13, usually 7 to 9, 

 muscular articulations. 



The pinnules of the first pah, Pi and P a are tolerably equal with 20-25 segments, 

 the lowest of which are broad and slightly keeled. The next pinnules slowly increase in 

 length and size and have the third and following segments expanded to cover the gonads, 

 which are protected ventrally by strong plates; the fourth and fifth segments are larger 

 than the rest, though not markedly so. This feature ceases rather beyond the first 

 third of the arm and the pinnules then become more slender, with the basal segments as 

 long as, or longer than, broad. 



The disk is 5 mm. in diameter, much incised and paved with small plates. The 

 ventral surface of the arms is moderately plated, and the pinnule ambulacra have dis- 

 tinct side plates with intervening sacculi, which are also abundant in the plating over 

 the gonads. 



In alcohol the arms are nearly white, the older ones a dark brownish gray. 



The preceding description is adapted from the original description of Carpenter, 

 with a few additions by Gislen and by myself based upon an examination of Carpenter's 

 two specimens. 



Notes. — The specimen from Albatross station 5367 has 18 arms; of the seven IIBr 

 series present six are 4(3+4) and one is 2, the last bearing externally a IIIBr 4(3+4) 

 series. 



The specimen in the British Museum from between Cebu and Leyte has 10 arms. 



