A MONOGRAPH OF THE EXISTING CRINOIDS 313 



Another specimen is similar, but the outer arms are rather smaller. 



A third is similar, but the outer arms are longer, reaching 20 mm. 



In all these specimens the length of the long inner arms is about 70 mm. 



The largest of the 5 young specimens from Siboga station 273 has the inner arms 

 45 mm. long and the longest outer arms 20 mm. in length. Some of the outer arms 

 are not so long as the pinnules which they bear. These last taper abruptly and are 

 composed of 6 brachials which decrease rapidly in width and do not bear pinnules, 

 terminating at the fourth segment of the first pinnule. The cirri are VII, 12, 6 mm. 

 long, very slender. All of the cirrus segments are subequal, rather more than half 

 again as long as broad, without dorsal processes. The cirri are confined to the inter- 

 radial angles of the centrodorsal, occurring in 2 pairs, with a single one at each of 

 the remaining three angles. 



A second specimen has the inner arms 40 mm. long and the outer up to 30 mm. 

 in length. The cirri are VIII, in 4 interradial pairs. 



A third example has the inner arms 40 mm. long and the outer up to 11 mm. in 

 length. The cirri are VII, three occurring singly and the others in 2 interradial pairs. 



A fourth has the inner arms 30 mm. long and the outer up to 10 mm. in length 

 from the axillary. The cirri are VII, resembhng those in the first described. 



The last has the inner arms 30 mm. long; none of the short arms are longer than 

 their first pinnule. 



All of the specimens which I have examined are light yellow brown in color. 



Notes. — Carpenter remarked that in the youngest specimens of this species which 

 he examined the centrodorsal is a thin and slightly convex circular disk about 2 mm. 

 in diameter which bears 5 pairs of cirri, 1 pair in each interradius. These cirri reach 

 6 mm. in length and consist of about 15 segments which are tolerably mature in their 

 general characters. 



The next stage is represented by a sUghtly older individual in which all the cirri 

 have fallen away from the centrodorsal and the obliteration of their sockets has 

 commenced. 



In another specimen this process has been carried further and the centrodorsal 

 has become more distinctly pentagonal, though it has progressed rather unequally, 

 some of the sockets being much more obliterated than others. 



In a later stage the centrodorsal is a thin pentagonal disk with the appearance 

 of processes at some of its angles which Carpenter saj^s are more probably, however, 

 the ends of the basal rays. 



In a full-grown specimen the surface of the centrodorsal is much more nearly 

 flush with that of the radials, though it still retains its pentagonal shape. 



In another case each angle of the pentagon is marked by a more or less deeply 

 impressed pit in which the basal ray is sometimes visible. 



Another specimen has a more rounded centrodorsal which is flush with the radials 

 at its edges and shows the basal rays at its angles, while there are indications of pits 

 at the distal angles of the sutures between the radials. The sides of the centro- 

 dorsal in this specimen are sHghtly concave, but this feature is much more marked 

 in 2 others in which the shape of the centrodorsal is markedly stellate. In the first 

 97298—31 21 



