PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 433 



8 mm. in interradial length. Except for a small area about the apex it is completely 

 covered with cirrus sockets, which are arranged in closely crowded alternating rows, 

 those of the succeeding rows becoming gradually smaller distally. 



The cirri are L-CC, 30-65, from 40 to 130 mm. in length. In some specimens the 

 longer cirri have the first three segments broader than long, the fourth about as long 

 as broad, and those following up to twice as long as broad, the length slowly decreas- 

 ing towards the tip. In others the segments are relatively longer, the first segment very 

 short, the second about as long as broad, the third longer than broad, and the follow- 

 ing ones increasing in length to a maximum of four times as long as broad; the outer- 

 most segments are shorter again, becoming terminally about as long as broad, with 

 slightly prominent ends. The opposing spine may be either absent, small, or well- 

 developed, and the terminal claw is slender, sharp, and moderately curved. The apical 

 cirri have 25 to 30 segments and are from 15 to 30 mm. long. 



The ends of the basal rays are just visible as small transversely elongate tubercles 

 under the interradial radials. 



The radials in the most fully developed specimens are just visible beyond the rim 

 of the centrodorsal; they are more extensively visible hi the immature, in which the 

 interradial radials are slightly longer than the radial radials. The distal edge of the 

 radials is slightly concave, and their lateral edges are wholly in contact with those 

 of their neighbors. The IBr t are twice as broad as long, not quite, or just, in contact 

 with each other at the proximal angles, with the lateral edges almost straight or more 

 or less convergent, in the best developed specimens with the distal border almost 

 straight, in the less developed with it deeply incised by a posterior projection from the 

 axillary. The IBr 2 in the most mature specimens are large and widely rhombic, 

 broader than long, about 5 mm. in width and 3.2 mm. in length; in smaller individuals 

 they are relatively much longer and shield-shaped, in the specimens from the Gauss 

 collection being 2.5 mm. wide and 3.0 mm. long. The median portion proximal to a 

 line between the lateral angles is more or less swollen. In immature specimens the 

 axillaries borne on the radial radials are relatively slightly longer than those on the 

 interradial radials. The variation in form of the radials and division series has been 

 illustrated by Dr. John in his Discovery Report, (1938). 



The 20 arms are up to 250 mm. in length. In the larger specimens the first 

 brachials are twice as broad as long, about twice as long exteriorly as interiorly, just 

 in contact by the inner proximal angles, with the distal border almost straight or slightly 

 concave; in less mature specimens they are deeply incised by the posterior process of 

 the second brachials. The second brachials are as long as broad, or in the less de- 

 veloped specimens longer than broad and shield-shaped with a long posterior process. 

 The first syzygial pair (composed of brachials 3+4) is about as long as broad, slightly 

 constricted centrally in the larger, more strongly constricted centrally in the smaller 

 individuals. The following brachials to the thirteenth or sixteenth have approxi- 

 mately parallel ends, and then* length in fully mature specimens is about three-fourths 

 of their width. The following brachials become triangular, distally gradually becoming 

 wedge-shaped and longer. 



In the smaller specimens the dorsal surface of the radials, ossicles of the IBr series 

 and lower brachials is often thickly covered with short spines; after the fifth brachial 

 these spines become longer and more prominent, and become restricted within a tri- 

 angular area, of which the distal edge, now somewhat produced, forms one side and the 



