A MONOGRAPH OF THE EXISTING CRrNOIDS 305 



segments, the width of the pinnule decreases more or less abruptly, a feature not ob- 

 served in var. insculpta; but Hartlaub remarked it should be noted that in some pin- 

 nules such an abrupt decrease in width is not marked. In contrast to the conditions 

 in var. insculpta, the following pinnules as far as P 4 are of the same length as Pi, though 

 with fewer (18-20) segments. Regarding the form of these pinnules, it may only be 

 said in general that they are composed of five broad and short segments, followed by 

 elongated ones. The first three or four segments are conspicuously carinate, though 

 in this feature there is great variation. The carination is sometimes more double, 

 sometimes more single; sometimes the crest of the carination is beset with teeth. When 

 gonads are developed — appearing first on P 4 — the segments over the gonads, usually 

 the third and fourth, are broadened. From P 5 , which is 7 or 8 mm. long, the length 

 of the pinnules decreases. The pinnules of the tenth-fourteenth brachials are about 

 7 mm. long, that of the sixteenth brachial about 6 mm. The usual length of the pin- 

 nules of the middle of the arm, 5-6 mm., may be reached with the pinnule of the eighth 

 brachial. Typical for the middle of the arm are pinnules with two short basal segments 

 followed by usually 10, rarely 11, elongate ones. Most numerous by far are pinnules 

 6 mm. long with 12 segments, in marked contrast to var. insculpta in which the usual 

 pinnules are 3 mm. long with 9 segments. If gonads are developed here — strongly 

 swollen gonads are lacking — the third and fourth segments are broadened. Toward 

 the arm tips, on the seventieth to eightieth brachials, the pinnules become more slender; 

 there is no decrease in the number of their segments, or increase in their length. 



The ambulacral plating consists of side and covering plates. The sacculi are 

 rather small and inconspicuous. The disk is deeply incised. 



In the specimen from Blake station 219 the centrodorsal is hemispherical and rather 

 high. Interradial ridges are here and there evident, as in those just described. 



The cirri are XXXII, about 20, longer than those in the specimens described 

 above. The first three or four segments are short, and an opposing spine is present. 



There are 10 IIBr 2 series, and therefore 20 arms. 



The first syzygy is always between brachials 3+4, the second from between bra<hi- 

 als 10 + 11 to between brachials 17+18, the next after an interval of from 5 to 12, 

 usually 8, muscular articulations, and the distal intersyzygial interval is from 7 to 10, 

 usually 7 or 8, muscular articulations. On one arm the second syzygy is between 

 brachials 8 + 9 and the third between brachials 34+35. In general the distribution of 

 the syzygies strongly recalls that of the three preceding specimens. 



P, is 8-9 mm. long with 20-25 segments of which the first seven are broad and 

 those from the second onward are doubly keeled. In some cases this pinnule is only 

 5 or 6 mm. long, apparently as a result of imperfect regeneration. The shape of the 

 proximal segments varies from that in the corresponding pinnule in the preceding speci- 

 mens only in that the keels on the proximal segments are broader. The pinnules 

 following up to P 3 on the arms studied are shorter, 6-7 mm. long, that of the sixth 

 brachial even 5 mm. long. In two cases the pinnule of the eighth brachial was found 

 to be exceptionally long, 8 and 9 mm., and in one case barely 4 nun. long showing, how- 

 ever, clear indications of incomplete regeneration. In view of these varying conditions 

 in the pinnule of the eighth brachial, Hartlaub was inclined to assume that, as in the 

 case of the three specimens described, the pinnules as far as the eighth brachial are 

 normally of the same length as P, and that the abnormal conditions were the result of 



