A MONOGRAPH OF THE EXISTING CRINOIDS 211 



mm. long; one of the IBr series bears two undivided arms, and three others have one 

 divided and one undivided derivative. There are 4 internally developed IIIBr 

 series, and 2 IIIBr series on a single IIBr series; the only external IIIBr series 

 is 2 instead of, as the others, 3 (2 + 3). The other example with 22 arms has the 

 2 posterior rays and their derivatives less than half the size of the remainder; there 

 are 3 IIIBr series, all internal and all 3 (2 + 3). The specimen with 23 arms has 

 the right anterior ray and its derivatives very small, and the anterior of about the 

 same size; the left anterior is slightly larger, and the two posterior are normal. All 

 of the small rays bear 4 arms each, the right anterior and the anterior carrying 2 IIBr 

 2 series, and the left anterior 2 IIBr 4 (3 + 4) series; the IIIBr series are internal. 

 The example with 18 arms has 4 of the IIBr series 2, and four 4 (3+4). The speci- 

 men with 17 arms has one ray with only IBr series, and on another ray an undivided 

 arm springing from a IBr axillary. One of the specimens with 13 arms has on one 

 ray two IIBr 2 series, one of which bears externally a IIIBr 3 (2 + 3) series. The 

 other has one IIIBr series. One of those with 14 arms has 3 IIIBr series, two of 

 which are on a single IIBr series, while the other is externally developed. One of 

 the 12-armed individuals has one of the IIBr series 2 and the other 4 (3 + 4); one of 

 the 10-armed examples is of mature size. 



The specimen from Siboga station 322 is large, with 16 arms 125 mm. long; the 

 cirri are rather small and slender, XVI, 21, from 15 to 17 mm. long. 



Extraordinary variability appears to be characteristic of this form. The arms 

 vary from 10 to 32 in number. The cirri are usually very slender, with the distal 

 segments longer than broad and bearing single dorsal spines, but they may be stouter, 

 with the distal segments not longer than broad, in which case they bear two dorsal 

 spines, a distal and a proximal. 



Abnormalities. — In one of the specimens from Siboga station 320, only a single 

 cirrus is present, the centrodorsal approaching the condition of a sunken stellate 

 plate. 



In a specimen from Siboga station 166 some of the cirri have the outermost 

 segments bearing dorsaUy a transverse ridge, with a small but distinct spine in the 

 center. 



In another specimen from Siboga station 166 one of the IIBr series is 2; in 

 another from Siboga station 318 one of the IIBr series is 2; in an example from 

 Siboga station 320 there are four IIBr 2 series and two IIBr 4 (3 + 4) series; another 

 from the same station has four IIBr 2 and four IIBr 4 (3 + 4) series; in a third the 

 only two IIBr series present are 2; while in a fourth there is one IIBr 2 series and 

 one IIBr 4 (3+4) series. 



In a specimen from Siboga station 318 one of the IIBr series is 1. 



In an example from Siboga station 320 one of the IIBr series is 3 (2 + 3). 



In one of the specimens from Siboga station 318 one of the IBr series terminates 

 in a trapezoidal ossicle bearing 4 arms. 



A IIIBr 2 series, internally developed, is borne on a IIBr 2 series in a specimen 

 from Siboga station 166; an externally developed IIIBr 2 series occurs in an individual 

 from Siboga station 320. 



