A MONOGRAPH OF THE EXISTING CRINOIDS 



745 



Description. — The centrodorsal is hemispherical to only sliglitly convex, almost 

 completely covered with closely crowded cirrus sockets of which the apical are not very 

 much smaller that the peripheral. The usually rather small polar area is more or less 

 concave. 



The cirri are XI^L, 18-22 (usually about 20), from 25 to 35 mm. long. (Note 

 BY A.M.C. In the type specimen of Antedon ciliafa there are about LXX cirrus sockets.] 

 The first seginent is short, the second is rather longer than broad, the third is rather 

 more than twice as long as broad, and the fifth, which is the longest, is about four times 

 as long as broad. The following segments are similar; after about the eleventh the 

 segments very gradually decrease in length so that the antepenultimate is about twice 

 as long as broad and the penultimate is about half again as long as broad. The oppos- 

 ing spine is small, usually about a quarter the width of the penultimate segment in 

 length, terminally sitvated and directed obliquely forward. The terminal claw is about 

 as long as the penultimate segment, moderately stout and moderately curved. The 

 cirri are laterally compressed for their entire length, this condition gradually becoming 

 more marked distally. The distal ends of the segments are slightly enlarged, and the 

 median portion of the distal border dorsally tends to project somewhat. 



The distal edges of the radials are even with the rim of the centrodorsal. The 

 IBr, are short, three or four times as broad as the lateral length, broader proximally 

 than distally, with the distal border sligiitly concave and rising to a small rounded 

 tubercle with the posterior border of the IBr2; the sides are rounded, and each IBr, 

 is widely separated from those on adjacent radials. The IBrj (axillaries) are pentagonal, 

 about as broad as long. 



The 10 arms are from 110 to 1.30 mm. in length. The first brachials are short, 

 over twice as long exteriorly as interiorly, with the distal border concave; the interior 

 edges are united for about half their length, the united and free portions of these edges 

 being at right angles to each other. The second brachials are much larger, irregularly 

 quadrate, with a convex posterior border incising the first. The first syzygial pair 



4 nnm 



Figure 47. — Thaumalomeira Unuis (A.H. Clark), type of Anudon cUiaUj, U.S.N. M., 

 22616, Albatross station 4982: a. Lateral view of calyx; b, tip of peripheral cirrus; 

 c, tip of apical cirrus; d, proximal part of Pj. 



